Suddenly remembering something you said days ago and realizing it sounds rude/negative/insulting/ungrateful.
Fearing that you have a personality which dooms you to sounding mean when you don't mean to be.
Being chronically behind in your schoolwork - so far behind, marching into the afterlife and retrieving Spenser to have him write a paper on himself seems easier than catching up.
Knowing without a doubt that, at least physically, your best years are behind you.
Ok, now I've really gone and depressed myself... *sigh*