The former two-division UFC champion is already regarded as one of the most talented fighters to ever step foot in the Octagon, but even so, fans are left with the impression that Penn never quite lived up to his full potential.
Cardio issues have plagued Penn throughout his career, which has caused outsiders to question his overall work ethic and motivation.
In the first five minutes of a fight, Penn is easily one of the most dangerous fighters in the world. Unfortunately, longtime fans have become accustomed to seeing him open up strong and wilt as the bout drags into deeper waters.
It's easy to forget how sharp Penn can be in the first round of a fight. His loss to Nick Diaz serves as a great example. From the looks of Penn's face and the final two rounds, it's hard to fathom the fact that he actually won the first round of that fight.
What about the draw with Jon Fitch?
Penn surprised the perennial welterweight contender with takedowns and suffocating top control to steal the first round of their fight.
The conditioning woes for Penn go as far back as 2006, when he suffered back to back losses to Georges St-Pierre and Matt Hughes. Penn won the first round of both of those bouts fairly handily, but his momentum began to taper in the later rounds.
As fans of the sport, it's easy to become disillusioned by the outcome and propose misguided solutions. Penn isn't some washed up scrub hanging on well past his prime.
At 33 years old, he still has one of the best chins in all of MMA, and his skill set remains world class across the board.
Whether or not you believe he's the best first-round fighter in MMA history, it doesn't take a trained eye to see the untapped potential lying within Penn.
What if he could sustain his first-round pace over the course of an entire fight?
If that were the case, "The Prodigy" would be sitting in a much better place than he is now.