Have you ever wondered why the most annoying songs get stuck in your head?

Or why do unfinished tasks circle and circle in your mind causing stress?

Or, how about -- why, when you hear the notes for "Shave and a haircut," -- do you instantly want to sing "two bits"?

Would you believe it if I told you these questions all had the same answer? I'll give it to you in a second -- but first, let me tell you why this matters.