Who didn't know that Zhai Sheng worked extremely hard when he was young? Even the competitors who hated Zhai Sheng could only concede defeat to him for the military merits he had built when he was young. However, compared to these merits, Zhai Sheng had suffered more injuries from back then.
These injuries didn't have eyes. They wouldn't know which parts of Zhai Sheng's body they could injure and which they should avoid. As such, who could say with certainty that Zhai Sheng didn't injure himself in that area when he was young and working hard and was still a normal man?
To put it crudely, if Zhai Sheng was a normal man and coupled with the fact that he was a soldier, his woman would generally not fancy other men after having tasted the fierceness of a soldier in bed.