You also have to understand, however, that when you are playing Vayne of all AD carries, you could be doing everything by the book and still lose. This is because Vayne is one of the most team-reliant AD carries amongst all of them. Your job is indeed to stay in the back and attack whoever comes first, but as you said, sometiems your team melts before you have time to do any damage, even if you stay in the back. This, then, comes down to issues of team composition and so forth. That is why it is sometimes very risky to play Vayne in Solo Queue because you rely a lot on your team, and if your team fails, there is not much you can do, even if you stay in the back, if everyone dies too fast, because with Vayne you always have to get up close and personal and auto attack from very close range. This problem is lessened with AD carries such as Graves (who can burst) and Cait who has gigantic range. As Candy Panda said, I really think Vayne is the hardest AD carry to master, and probably not the best one to be practicing the role on.