I've always wondered...

Do the contestants that ever participate in these types of shows ever watch them first? Like, when you sign up for a Bear Grylls reality show, have you ever watched him in his series first to get some pointers? The first episode has a guy jump into a cold river with his clothes on. If you ever watched Man Vs Wild, Bear always says to take as many clothes off as you can. I just don't understand these contestants.