You're assuming they all fall behind. I attended KCPD's in 1981 and it was fully as intense as the MI outfit described above. In those days, if the 'washout rate' was below a certain percent, they figured the training wasn't tough enough.
IIRC, we started with 26 and finished with 12 or 13.
I'm inclined to think if a man hasn't gotten his point across in 4912 attempts, 4913 probably isn't going to do it.