...The list is probably a mile long. ^^; I look forward to reading the replies~
But here's mine: I wish people understood that a last-minute idea, or even just a later idea that's added to a story concept, isn't automatically worse or less valid or an 'afterthought'.
Even people who are writers themselves seem to subscribe to this idea when judging other people's work, and I think it's really...silly and unrealistic. =/
The notion that the only good ideas are the ones that are planned from the very beginning just doesn't make sense in several contexts...like a context where 'pantsers' exist. Or where multiple drafts exist. o_0 If you stop to think about this "criticism" for just a few seconds, it immediately falls apart.
Firstly: all writers make changes to their stories as they develop. Your first idea isn't always your best one, and the vast majority of ideas need a little work to become the best versions of themselves. It makes COMPLETE AND TOTAL SENSE that a writer would make changes to a concept to get it closer to what they want for their story; there is nothing inherently wrong with this. And if not for the fandom obsession with getting to see 'behind the scenes' on every little thing, I bet 90% of the time you wouldn't even notice.
Secondly: I will admit that a last-minute decision that feels last-minute is a valid thing to criticize.
Like, if you were to say "this magic item is poorly worked into the plot and feels like a Deus Ex Machina; and the fact that the author claims they came up with it 2 days before sending it to their editor seems to explain a lot" <-- I can accept that.
But-- and this may be an unpopular opinion-- the fact that the idea was last-minute isn't automatically the reason why it sucked in execution.
What I mean is, clearly it was a last-minute idea, AND the author figured it would be fine if the idea had no setup. Or, it was a last-minute idea, AND the author underestimated how long it would take for them to write it in properly, rushed through the process, and made the end product worse.
My point is, the timing of the idea clearly wasn't the only thing affecting its quality. I'm a pretty daredevilish pantser, and even I know when it's too late to work in a new idea before a deadline.
Part of becoming a mature writer is learning how to resist temptation and just leave things on the cutting room floor, no matter WHEN you come up with them (i.e. basic editing). Not being able to do that will cause more problems than last-minute ideas ever will...
Thirdly...believe it or not, some of us have skills. =P Maybe you can't fathom working a new idea into a story 2 chapters after the fact, or 10 chapters, or 50 chapters, but you gotta realize that not everyone is working under that limitation.
Some of us are super organized, some of us have great memories, some of us just know our stories and characters well enough to anticipate how a new concept will affect them, and edit accordingly. Some of us have none of those qualities, but are willing to put in the time and effort to make things work regardless. ^^;
In general, just because adopting a certain strategy would cause you to screw up your story/art doesn't mean that it should be forbidden for everyone. Save your judgement for the results, not the process.