Superstitions
You never knew. Cho'd seen too much in the world, too much not to have some belief in the unknown. Yeah, he'd probably join in if the others were making fun of say Van Pelt for some silly belief or other. But that was just a cover. Because really what harm did it do to be careful? So if he threw spilled salt over his shoulder, was watchful of ladders, avoided black cats and always avoided sidewalk cracks, what difference did it make? Cho knew very well that what you didn't know could indeed hurt you. Because you never knew.