I think it's more than that. It's a way of filtering people who can't handle the frustration of repeated failure and failing in spite of doing everything right. For elite soldiers like the SEALs, I can see how this would be valuable. There is a high risk of failure on their missions, as well as a high risk of capture, since they often operate behind enemy lines. The ability to handle persistent hardship without giving up could mean the difference between life and death.