Who said "I'm not very good at this."?

This quote is attributed to Marlin.

I'm not very good at this. - Marlin

"I'm not very good at this."

Marlin

"I'm sorry, but I can't help you. It's not you, it's me. Well, actually it is you."

"I promised I'd never let anything happen to him."

"He's my son."

"I have to find him. I have to find Nemo."