All cute little instructional writing-adages like this are crocks of shit, because once they get very well known, they also get very well misunderstood. The main problem is the whole truth of a matter can't be crammed into only a few words. There is always more to it, and exceptions to the rules; it gets messy to take these adages as being deep enough to reach any level of truth. There's a reason sayings are usually generic, because then they can be applied to everything. Good to sound wise. Bad to instruct how to write.
If you've been writing for a while and thinking seriously about writing, you've probably already started wondering what adages like these aren't telling you. And if you've checked around a writing blog or two you'll find that everyone has a very helpful instructional post on the miracles of 'show, don't tell' but very few of the posts actually tell you anything new or deeper other than basically repeating the mantra and defining the two terms involved and saying "ta-dah" when they've managed to state the obvious and pretend it proves itself.
Seriously, the first thing you should always do as a writer, when presented with advice or sage wisdom, is ask yourself (or the advicer/wisdomer when accessible) what you aren't being told. Figuring out what most of the writhing masses aren't able to figure out will help you be smarter than them, which is a good thing if you're trying to become a writer. It's competitive! Which is probably why many of the people who have figured these things out don't talk about them unless being paid a handsome salary to be a teacher.
So, what's wrong with 'show, don't tell' that we need to figure out? What makes it a crock of shit?
First off, had most of the blogs I've seen on this subject been posted back in old-timey days, they would have been revolutionary! The adage probably meant something at some point in literary history when everything was written Washington Irving style where you had a writer adopt a pen name and claiming to have found the lost papers of a gentleman who had written about a person he met in his travels who'd told him a very true story of a person or village. Most stories written from the days of yore were still very 'told' by a heavy narrator presence to the point of addressing readers directly via such clever mechanics as 'now, dear reader, as you read this tale of woe, keep in mind...'. This isn't as cool anymore. So while at some point in time 'showing' would have been a revolution in literary styling, these days it's actually not usually enough.
But what more could there be than showing?! Well, let me demonstrate while making fun of the typical example one can find littering the blogs of a million aspiring writers who also aspire to prescriptively inform other aspiring writers of what they've learned through their inspirational aspirations:
Don was angry.
Don's face turned red.
HOLY CRAP I can SEE he's angry because it's being SHOWN and not TOLD!!!
Here's the problem, the only reason you know he's angry is because I just 'told' you that in the prior sentence. Really, there are a million reasons someone's face can turn red.
Ah, but one must simply return to the trusty adage and SHOW even more of his anger, right?
Don's face turned red and he balled his fists.
There. Done, right?
Well, I don't know. The first problem is that this isn't unique, it's generic_angry_guy_action_07 plugged into our story to 'show' the character is angry. If you don't show the generic actions, it's confusing, and if you do show the 'easy to identify' actions then it's cliche. It's uninspired writing we've seen a million times in a million generic novels that usually still sold a million copies (but that's another rant all together). Another helpful hint: any actions readily done in Loony Toons cartoons should not be done in your fiction. I love cartoons, but they're meant to be funny, and when your characters start acting like they're in a cartoon, I laugh at them.
And just because a characters face is red and fists balled, it's still not clear. He could be scared. Could be having a heart attack. He might be angry enough to kill, or just frustrated at himself, or just embarrassed. So, these sorts of 'shown' actions that people default to, on top of being cliche usually, and still vague. (cue Whammy sound now)
What's a writer to do? Well, when a critique points out confusion over the emotion or experience that is being 'shown,' writers often first have their own faces turn red as they ball their fists. Then, this overly-defensive writer will often go back to what they know how to do so well, and try to prove you wrong by showing even more!!
This usually just becomes a bad game of literary 'show, don't tell' charades:
Writer, reads the card and writes: Don's face turned red.
Reader: Oh, ummm. I know! He's embarrassed.
Writer, frantically taps on what he's written.
Reader: ummm, Sunburned? He's half lobster? Why are you just pointing repeatedly to the thing I'm already clearly not understanding?! (wait, that's a Win, Lose or Draw motion, not charades... whatev!)
Writer, shakes his head, and writes: Don's face turned red and he balled his fists.
Reader: he's gonna fight someone!
Writer, rolls his eyes, and writes: Don's face turned red and he balled his fists, shaking them toward the heavens.
Reader: he's mad at his church and going to fight God?
Writer, does that palms up 'wtf?' pose, then writes: Don's face turned red and he balled his fists, then unballed them but still stomped around looking at the ground.
Reader: He got mad before, but is now trying to calm down.
Writer, does that charades 'come on, come on' rotating motion with his hands.
Reader: The guy was stung by a bee? Stubbed his toe? Found out his wife is cheating on him? His daughter IS a bee and stung him... ummm like metaphorically.
Writer, cracks and yells: NO YOU IDIOT HE'S JUST ANGRY!!!
Reader: Sheesh, why didn't you just say so! ......... ummm, why is he angry, though?
Writer, says: I was getting to that, but having a hard time showing the internal grief he feels over losing his son to street gangs... I was thinking maybe I'd have him stub his toe while ducking away from a bee. It would symbolize the...
Reader, closes book and doesn't want to play anymore.
Why does the reader close the book? Because the writer is becoming as cartoonishly comical as his character stomping around in circles like one of the Three Stooges insisting his own idiocy in conveying a clear meaning is the fault of the reader. A reader shouldn't have to fight with your prose to understand what it means. Good writing is clear writing (an adage that may not be a crock of shit?).
The last part of the charades had a point, though. In a story with any level of refinement, the reader is going to want to know WHY the character is angry. If the reason isn't any deeper than him stubbing his toe on a bee, then you've, at best, just written some slap stick comedy. I love Loony Toons, but is that what you're trying to write? Something the reader can laugh at? Not with, but at? Or do you want to build a character that isn't just the butt of jokes by delving into why the character is angry? How his anger feels? What does this anger mean to him? Is he scared that he's angry? Is he planning to kill someone now? Did he piss himself and we just can't 'see' it because it hasn't yet seeped through his britches enough to be 'shown?'
Answering these sorts of questions can elicit an emotional reaction from the reader. This is terrible for Loony Toons, as we hopefully wouldn't be so quick to laugh at Bugs Bunny if we empathized with his pain and humiliation. But eliciting emotional reactions through empathy for a character is a good idea for your fiction. Connecting a reader to the specific experience of the character is how the characters feel unique and real, and how your story becomes memorable and worth reading.
Ah, unique characters! Good idea! So, like, the character's face can turn green and he does the humpty-dance when angry?
Well, that's kind of cool, but no. If your first assumption was to simply come up with zanier (read as: even more confusing) external reactions, please go find your finest white gloves and smack yourself across the face with one of them. More showing that is even more ambiguous or confusing is never the answer!
What is the answer?
Answer: JUST TELL US WHAT THE HELL THE CHARACTER IS THINKING AND FEELING!
I know, it sounds so simple... because it is. The tragedy of the 'show, don't tell' mantra is that most internal thoughts or feelings need to be 'told,' from a technical standpoint, if you're pedantic enough, unless the character thinks in pictures he or others can see (ala the tattoo artist in the greatest RPG ever Planescape: Torment). So, novice writers avoid any and all internal character work, and simply 'show' the character being pushed around the set like a prop in a play.
And if your first thought was 'but I DID tell you what he was thinking or feeling with the sentence 'Don was angry' please see above regarding a glove and your face. That's not telling us what this very unique and specific character is thinking or feeling, that's telling us what a generic character could be thinking or feeling. Get into Don's psyche, explain how he feels when he's angry in this moment, and what he thinks, and what he is experiencing... that way, the reader at least has a chance to understand and empathize with what he's going through.
And no, this doesn't mean to change the sentence to:
Don felt his face turn red.
But nice try, you sneaky devil!
Dig deeper. Bring us the unique perspective of this character so we can get some insight into his psyche. Don't just 'show' Don running around like an idiot in a cartoon. And don't just tell he could feel his face turn red, unless he was previously paralyze in the face, as it would then be very relevant that he could feel his face again. Whether you show or tell doesn't matter, the important thing is that you recreate the truth of his experience as he's experiencing it, so we can experience it too.
Easy, right? Now do it!
My 'show, don't tell' advice: show yourself a well written book, then tell yourself to read it. Then show yourself your writing, and tell yourself how it can be better. Then show yourself the same well written book, but this time tell yourself to study it. Pay attention to how good writers capture the truth of a moment, how they build empathy through a character's experience so the reader can experience it too (not just watch the show, but feel IN the show), how the best writers can pinpoint exactly how a character is feeling or thinking or experiencing the world.
And if you're really paying attention, you'll soon realize you've completely forgotten the flawed, irrelevant adage 'show, don't tell.' Then, the next aspiring-writer-doling-out-advice-to-aspiring-writers blog you come across trumpeting the virtues of 'show, don't tell' will make your face turn red and you'll ball up your fists. You're angry! Right? No. You're upset that so many aspiring writers seem too willing to puff up their chests, write about all the things they know, and advise others to cling to inadequate adages like 'show, don't tell' when it's a huge crock of shit.