There all foolish. It does not change a thing whether you get it or not. Ive done the raid many times on my 3 characters and I never leave that chest un opened. People are superstitious that the chest puts timers on other chest and or lowers the percentage of getting good gear. But I'll be honest, I've gotten at least 4-5 Vex Mythos, Countless times gotten 2 raid helms from 1 atheon kill, I've gotten Plan C, Suros, P&T and Ice Breaker from chests on Hard and Normal. So pretty much its all RNG and nothing to do with the chest.