running out of oxygen can cause a blackout. >> trubridge: ( grunting ) >> simon: the sound you are hearing is william ( grunting ) >> simon: he's made it. but for his record of 410 feet to be ratified by the judges, he needs to perform three simple tasks when he gets to the surface---- take his goggles off, give the okay sign with his fingers, and say i'm okay, in that precise order. sounds simple, but william's brain isn't working. he does these things in the wrong order. the judges disqualify him. >> linden wolbert: he took off the nose clip, made the sign, and said "i'm okay" without removing his goggles. >> simon: boy, oh, boy. he had just been down a quarter of a kilometer. >> wolbert: that's correct. >> simon: he did goggles in the wrong order and it cost him his record. >> wolbert: it did. >> simon: it sounds like a technicality, but he has to prove that his mind is as tough as his body. you got there. you got... you got deeper than anyone has ever gotten before. >> trubridge: yeah. yeah. >> simon: and then, you took your mask off and said okay in the wrong order, and it was all for nothing. >