In boxing, almost everybody loses eventually. The fighters routinely mentioned in debates about the all-time, pound-for-pound greatest boxer all had multiple losses on their records.
Of the handful of fighters to hang up the gloves without a loss, only Rocky Marciano, Joe Calzaghe and Ricardo Lopez are viewed as Hall of Fame-level guys. But Marciano and Calzaghe both receive legitimate scrutiny for the quality of their resumes, and Lopez hammered out his record of dominance at the minimum weight of 105 pounds. Fair or not, a guy that size is never going to get full consideration from writers or fans.
The fighters who have achieved the greatest glory in the ring have all had to drink from the bitter cup of defeat. So it shouldn't be surprising that whenever an undefeated boxing phenom arises on the scene, fans start to speculate on how much longer he can retain the zero in the loss column.
Disregarding Chris John, I view 13 undefeated fighter as within or very close to the active pound-for-pound top 25. I am excluding John because I don't have enough insight into his career to cover him in this article.
I read and write about the other 13 weekly. I've seen their most recent fights and signature performances. If I don't know whom they are fighting next, I at least have a good hunch. I have a good idea of who is most likely to threaten their perfection.
None of these guys are prospects anymore. Even the youngest on the list has world champion status. And sooner or later, most of them are going to lose.