Weird thought of the day:
“Don't knock it til you try it.” is probably an expression created by house thieves.
I picture two guys - with masks on - hiding in the bushes outside a house. One of the guys gets up and is about to knock on the door...
"Whoa! Whoa! Whoa! Steve! What are you doing!?"
"What? I figured I'd knock, Bill. You know, to see if anyone’s home."
"No, Steve! Don't knock it til you try it!"
*Steve turns the doorknob*
"Ha! Good call, Bill. It's unlocked! Sweet!"