You forgot to bring your homework again. How come?
How come your little sister is so angry?
How come we were not invited to the party?
A: Are you going to your sister’s wedding?
B: I decided not to go.
A: How come you’re not going?
B: Because I’m afraid that if I go I’ll catch the bouquet of flowers and then I’ll have to get married.
A: Don’t be silly. Just make sure you don’t catch it.
B: Hey, that’s a good idea. I never thought of that.