if i remember well:
on krasiviy: he is good-looking (and is usually always good-looking).
on krasiv: today, he looks good.
on bolnoy: he has a serious illness and may never recover.
on bolen: he' ill for the moment and for the moment only.
so the long adjective is used when you want to describe a permanent or long lasting conditions, the short one is for temporary conditions.
but people say:
ia grustniy when it's clearly not going to last forever.
why not ia grusten?
it seems to me like most of the time, the short form doesn't even exist (what about miliy, dobriy, khoroshiy?) and that is making me completely lost:/
can someone please clarify that a bit for me?