Stumbling on other people's dumbness

"I know. I'm just like a chair you stumble over in the dark." Elizabeth said. "It isn't the chair's fault, but you kick it anyhow."

Nat blinked.  "What are you talking about?"

"Your brain. It's too fast.  So you stumble on other people's dumbness.  And - you want to kick something." 

Nat felt his face get hot.  "But I shouldn't."

Elizabeth agreed.  "No you shouldn't, because even if people are dumb, they aren't chairs, are they?  They do have feelings."

Carry On Mr. Bowditch - Jean Lee Latham (pg 82-83)