In my very first game (playing as Garen), I didn't understand why my friend was telling me to buy a bow (Last Whisper) as a sword user. I was immediately ashamed when he explained it to me. When I was just generally new to the game, I didn't understand hot to build based on how the game was going. It was more or less just build pure damage or pure tank based on who I played.
What was your misconception that you're ashamed of?