Throwing weapons

I just want to ask, what stops me from throwing anything? I get it, it's hard and not so efficient to throw a sword, but after martial charaters starts doing inhuman things, i don't think throwing anything could be an issue. Am i just lacking knowledge and there is a certain rule. Also considering improwised weapon, what counts as throwabel, and how do you decide what stat to use for it?
While on the topic, i figure creatures who can't throw irl can't throw in game, or i don't know how that work.

Yes, this did come up last session, don't ask.