I saw Derren Brown perform a trick in which he stated that it was proven in maths that changing your mind is the better thing to do. He presents 3 boxes, you p

I saw Derren Brown perform a trick in which he stated that it was proven in maths that changing your mind is the better thing to do. He presents 3 boxes, you pick one. He eliminates one and asks if you want to change. You are going from a 33% chance to a 50% chance, plus most people think they are being double bluffed.