Things that took you forever to find out?

Alright, just had a 65 minute game, pretty epic back and forth game where both teams had multiple inhibs down at the same time multiple times. Anyway, end of game is coming along and we catch out their mao, our team has no nexus turrets and I see their kalista running up mid. Now I know that we are fine killing mao before she gets there and I can tele back to the nexus right? WRONG. I have almost 4k games played and tonight I found out that you cannot teleport to the nexus. Pretty sad way to go out of what was a crazy game, but at least now I know.

Now that I have shared, anyone else learn something like this after years of playing?