Julian believes that if Jack loses all of his friends it will serve as a _____ ____ _____?

From the text:

"I know. Anyway, Julian said that he thinks being friends with Auggie is bringing you down, and that for your own good you need to stop hanging out with him so much. And if you start losing all your old friends, it'll be like a big wake-up call. So basically, for your own good, he's going to stop being your friend completely."