better than sterilization.... I didn't expect that
This is probably because surgery is always a tradeoff: You want to get the job done, but you don't want to go crazy with the scalpel and cause unrelated injuries. In the case of vasectomies, men usually want the smallest possible cut to be made, to the point that it's not necessarily obvious whether the procedure was completed.
For a really scary example of how surgeries can fail: Surgical abortions have a 0.2% failure rate. You might think that an adult armed with a sharp knife should be able to kill a fetus rather more than 99.8% of the time -- but the added requirement of not killing the mother clearly makes things more difficult.
This is probably because surgery is always a tradeoff: You want to get the job done, but you don't want to go crazy with the scalpel and cause unrelated injuries. In the case of vasectomies, men usually want the smallest possible cut to be made, to the point that it's not necessarily obvious whether the procedure was completed.
For a really scary example of how surgeries can fail: Surgical abortions have a 0.2% failure rate. You might think that an adult armed with a sharp knife should be able to kill a fetus rather more than 99.8% of the time -- but the added requirement of not killing the mother clearly makes things more difficult.