The Problem With Vayne
When you are playing against Vayne and she gets fed or to late game and starts destroying your whole team, you feel so helpless and disgusted that you don't really wanna play anymore.
When you are playing Vayne and you get destroyed before 20 minutes and can't even build static shiv before the nexus is torn down you feel like garbage and don't wanna play anymore.
Basically, 95% of games that Vayne is played in someone is gonna feel like helpless trash and not enjoy the game at all. Where there's only like 5% of games where it's actually a fair, fun, and competitive match. Though this can be true for most champions, the champion that this is the absolute worst for has to be Vayne.
