Does it really work to swear that you can't get into graduate school?

Swearing is just a psychological hint of self. Do what you should do. Let it be. But don't swear easily, because swearing is likely to cause some psychological pressure on yourself and make you unhappy.

Oath is only the binding force of words, and it is fragile! Especially the vows made easily, don't take them seriously, because they are usually emotional.