A question i get far too often, and not only when I play Miss Fortune .
I also get flamed a lot because of that.
On ad carries that have no escapes i build botrk to help me escape, it's simple.
A xin zhao jumps you ? Just activate botrk and he won't be able to get the 3rd aa to knock you up.
It saved me loads and loads of times, it even saved me from a garen ultimate once, the dude ulted me and expected me to die, so he turned away from me, but i botrk`ed him right before he ulted and i escaped with like 20 hp or something due to the heal i got from it.
And i also get it on Ashe/Twitch/Varus/Jinx and sometimes Sivir