Usopp had self image issues, this was clear. He always had a reason to seek you out, to cry into your hands, to beg for something, anything. He always compared himself to an angel, never a god like others would.

"I was always just an angel, never a god- you understand, right?" He said through tears. "I'll never be as good as a god. Im just an angel, a useless one at that."

You just ran your fingers through his hair, decoding his words. He couldn't live up to his high expectations, his expectations to be a "god".

"Don't say that.." You murmur. "I'm not wrong though, am I?" He barked back, crying into your shoulder.