Do your characters adapt? They ought to. Any tale, regardless of length, is about changes - after all nobody in life stays static so your characters shouldn’t. Your characters should develop as we do in life. It’s in that sense any fiction should mirror life.
Take your time going over your completed work, particularly if it’s a novel. Ensure everything makes sense, that the plot lines tie up and you know what’s happened to all your characters. It’s easy to forget a minor character - if you find this happens, ask yourself if you need them in your story after all.
Always take out what you can from your stories without losing the sense of them. It’ll make your writing tighter and quicken the pace. Less is always more.
Get into your characters’ heads as quickly as you can. Can you sum up their main characteristic in one or two words? Can you sum up your story in a line or two? Are your characters different so you can tell them apart? Do their voices sound different so nobody is confused as to who speaks?
Moments of weakness in a character can be used to strengthen their portrayal. We all have moments like this - fictional characters should reflect that. It is then what real and fictional people do after having such moments that can add or make a story.