The deal was set, he'd committed to buy, still not sure when his financing would be approved, but hey, if you have one foot on the boat, one on the dock, what can go wrong?
Used as a promise, and can be used instead of on God. It is a promise that isn't broken, guaranteeing something to someone.
Stan-"Do these shoes look alright on me, I wanna wear them to Stephens 80th birthday tomotomo"
Freddy-"yeah mate, they look great"
Stan-"promise?"
Freddy-"one gorilla"