Whats the thing you hated most, but made you learn the most?

For me it is all of those annoying top laners, lulu, ryze, lissandra, vayne, ect. When I first got back to league about a year ago I hated them. Lane phase was so frustrating. However now because I sat through all of these players not only is it super easy to lane as melee vs ranged, I can also lane swap and do well because I understand the concept of being in lane > cs.