Comment by Tangurena2

They get transferred to a different unit - one that is not part of "special forces". A big part of the selection process is to find the soldiers who just won't quit.

One rather famous example is of a BUD/S (usually called SEAL) selectee who drowned himself. When pulled out of the pool and resuscitated, he apologized and thought he failed out of the selection process. The instructor replied something like "heck no, you passed. We can always teach you how to swim. No one can teach you to never give up".

https://en.wikipedia.org/wiki/United_States_Navy_SEAL_select...