Someone else gets it.
This has always been Penn's problem, he has no heart. As soon as a fight doesn't go his way, thats it. He has no ability or will to come from behind. Like you say, Penn wins in the first round, or he has no chance.
Penn has plenty of heart and it showed in Diaz fight, he got beat up in the 2nd rd with one eye completely closed yet he still was walking forward in the 3rd and actually made it a close rd despite being gassed and hurt. the only time he has ever "quit" is when he is gassed and has a strong wrestler on top of him but there is not much you can do in that situation.