Short Mentors' Height Requirement

Listen up, genius. You see, the joke rely on the double meaning of the phrase "look up to." It literally means to raise your eyes to see someone taller, and figuratively means to admire or respect someone. Short people are, well, short, so you can't physically "look up to" them, playing on the idea that you also can't admire them as mentors. Get it now, smart guy?