Generally I'm afraid of watching series that are hailed by others as amazing/masterpiece/controversially awesome/disturbing/most original etc. Probably because I always feel shitty after watching them since it means there is now one less great series to watch. I'm also afraid of watching soap-opera-ish romance/slice-of-life (ie. Nana, Bokura ga Ita, Hachikuro) since there's a higher chance of me getting really emotional over the characters.
But I watch them anyway.