Already bought the kilt

A phrase used when pointing out that someone has already sunk too much effort into a situation to turn back or quit.

"I don't know if I can finish this degree, I don't even like economics..."
"dude, I know you're exhausted, but you can't quit now, you already bought the kilt."

"Why do you even want to be in his wedding if he's such a jerk? Just drop out!"
"I can't man, I have to go through with it, I already bought the kilt."