An Educational Experience
First some fun facts about the durability of testicles.
A testicle can theoretically take up to 60psi (pounds per square inch) before rupturing. If you are wondering how much pressure 60psi is, it is about the amount of force that a girl could produce if she squeezed about as hard as she could with her hands. This amount of pressure cannot be achieved accidentally simply by squeezing.
Aside from squeezing testicles they are very well protected in the scrotum. If brute force is used such as a punch or kick the testicles move out of the way within the scrotum. It is like trying to punch balls that are literally inside of jello. The harder the blow the more the testicles move away from the impact. Hitting a testicle dead-on is actually quite difficult.
Testicles are unlike anything in the human body. They are all give. Hitting them is like pushing a swing. Like the swings you might have played on as a child. No matter how hard you might have pushed that swing it was never going to break. Testicles are like that as well. No matter how hard the blow is they will just swing. There is no chance of breaking "the swing". Because the testicles swing on impact very little of the impact actually hits them. It is like trying to cut food after throwing it into the air. Things cut a lot better when they are stuck in place. Testicles receive very little damage from the impact of blows because of their ability to redirect the energy in the form of moving. Testicles are very sensitive but they are also quite durable toward most forms of attack.