One dictionary says ‘you’re on’ is used tell someone that you accept a bet or an invitation to compete against them. Then why does it use ‘you’ instead of ‘I’? What’s the ‘on’? In terms of the meaning, ‘I’m on’ is more understandable and easier to memorize, at least for me.
Just for your information, I found the phrase in the following scene.
”Yeah,” said Harry. “Yeah … we’ve helped each other out, haven’t we? We both got here. Let’s just take it together.”
For a moment, Cedric looked as though he couldn’t believe his ears; then his face split in a grin.
”You’re on,” he said. “Come here.” (Harry Potter 4 [US Version]: p.634) [Bold font is mine]
N.B.: Harry and Cedric are competing for the cup a few feet away from them, but they are friends now because they were helping each other during the tournament.
I have two questions on this phrase.
1. Why does the phrase use ‘you’, not ‘I’?
2. What’s the meaning of ‘on’?