I'm good in my head

Dominic purchased a lego ninja in the store today.

I overheard his ninjas talking.

"I'm really good at fighting! I've never done it, but I'm so good at it in my head that I just know I'll be good."

"I know what to do! Oh dear, that didn't work. I don't know what to do. You are just too good."

"I know, I'm awesome!"