"The fight game starts hard and ends harder. This is an almost universal truth. Five years after he realized he might be done, Penn should know for sure now.
His legacy won’t be left in numbers. These final losses made sure of that. If you need to analyze his record, you didn't see him at his best. And if you saw him at his best, you wouldn't need to analyze his record.
Penn was great. Penn was game. And to the end, Penn refused to stop taking on challenges that appeared unconquerable because...because just scrap. That’s why."
A guy by the name of Mike Chiappetta wrote that after the Yair fight, it's part of one of my favorite articles.
I can't tell you why others consider Penn an all time great, but I'll tell you why he's an all time great to me.
I've been a combat sports fan for a while now. When I was a kid, my Dad told me about Riddick Bowe tossing his belt in the trash to avoid fighting Lennox. In my lifetime, I've seen Chuck/Wand happen years after it originally should have. I saw Mayweather and Pacquiao dance around eachother and play the blame game for literally half a decade. I saw Canelo hold out on fighting GGG until he started to slip a bit. I saw GSP not want anything to do with fighting Anderson even when presented with the offer of a catchweight fight. I saw Anderson want nothing to do with the idea of a Jones fight during the time that was on the table. We just saw a heavyweight superfight go up in flames in Joshua/Wilder because of shenanigans. Roy Jones and Tiger never happened because of this, that, or the other. DJ didn't want to fight TJ. Rhonda and Cyborg would constantly get at eachother throats, but a deal could never be reached. I'm forgetting a bunch, I'm sure.
Penn, for all his flaws, never once held up a big fight. He wanted to fight the best fighters available, regardless of anything else. He didn't care about weight classes, where the fight was held, how much he was going to be paid, or how a potential loss would effect his legacy or earning potential.
When Penn got offered the GSP II fight, I guarantee he didn't think about anything except that he wanted the fight. He got the fight. And ten years later, a lot of people still refer to it as the biggest fight in UFC history.
GSP had the opportunity to do the same thing with Anderson, but instead of signing on the dotted line, he weighed the pros and cons, and decided it was a bad choice. Now maybe he was right and maybe he was wrong, but regardless, we never got the fight. And we, the fans, wanted the fight.
BJ gave the fans what they wanted to see, and that's what his fans remember about him. So, when you see someone say "oh well BJ fought outside of his weight class" it isn't an excuse, it's the truth. You don't see fighters that are stars (and trust me, Penn was a star) take the legacy altering risks that he took.