I'm tired of people saying "I could sleep on a park bench and I'd still happily play for England". I'm sure you would. But you'd be shit.
Because at the highest level the margins for error are tiny. Everything makes a difference.
If Lucozade could guarantee that "if you drink nothing but Lucozade Sport for six months you will cut a tenth of a second off your 100m time" would that make any difference to me? Hell, no. You could shave ten seconds of my 100m time and it would still be crap. Now pose the same scenario to Asafa Powell. That same tenth of a second is the difference between Gold and Nowt.
Likewise, if I play footie after staying up till six in the morning, off my face, it's quite likely that someone from the Leeds University football team will do an "Escape to Victory" flick over my head and score. If I had a good night's kip beforehand, it's quite likely that someone from the Leeds University football team will do an "Escape to Victory" flick over my head and score. Please note, this is an entirely made up example. Honest. But a good night's kip could be the difference between John Terry mistiming his tackle and giving away a penalty and getting it right and making block of the tournament.
Hopefully it won't matter against Trinidad and Tobago. But against the Argentinas and Brazils of this world, those tiny margins are the difference between shame and victory.