I respectfully disagree. You can't just force your mind to continue learning for as long as you want it to. There is a threshold. If you're at something for too long, your mind starts to become overwhelmed and you stop comprehending as well. Like when a computer has too many applications open and starts to freeze up, it needs a reset. I usually take a quick nap to reset, then go at it again unless I feel myself too wrapped up in whatever I'm learning, then I just play some video games or get out or just anything where I can throw myself mentally into a different environment and continue whatever it is I'm learning, the next day. This is why I would attribute the main reason for BJ Penn getting good is not from repetition (even though it was probably a factor, just like being flexible, strength, speed etc... are factors) but from his unwavering competitiveness and momentum. He aims high, then once he reaches there, he aims higher and still has everything fresh in his mind. If he's losing in the boxing aspect, rather than taking it to the ground, he tries to beat them in the boxing. Others give up to quickly IMO, where as people like BJ Penn don't know when to give up. There's good and bad about both but you can have both by always being honest with yourself. Anyways, point is, it's not all about putting mindless hours of physical repetition in, otherwise you would never see white or blue belts who have been there for 6+ years and I know a lot of them.