What happens if you fail SAS selection?
Most people who attempt SAS reserve selection do not get through, and the majority come unstuck for preventable reasons — feet, food, pacing and preparation — rather than raw ability. People do reapply, and a failed attempt is worth far more than never having gone if you are honest about what actually stopped you.
Why people actually fail
From what I watched: boots that had not been broken in, a bergen loaded heavy too early in training, nothing eaten in the first hours, and going off too fast on the first climb because everyone else did. Each of those is decided weeks earlier, not on the day.
Voluntary withdrawal is the quiet one
Nobody plans to stop. What happens is that the discomfort becomes constant and the reason for continuing becomes abstract. If you have never deliberately finished a session you wanted to quit, the first time you try it will be the worst possible moment.
Can you reapply?
People do go back. Whether and when you can is something the unit will tell you and it depends on circumstances, so ask them rather than a forum. What is in your hands is what changes between attempts.
How to use a failed attempt
Write down, that week, exactly what went wrong in order and at what point. Memory sands the edges off within a month. Then fix the two biggest items properly — usually base fitness and load tolerance — before touching anything else.
A note on accuracy
Entry criteria, standards and selection dates are set by the Army and change over time. Take anything current from the Army's own UK Special Forces Reserve pages; take everything below as one applicant's experience.
Get my 21 SAS reserve selection prep guide
What the stages are, what I was training to before I applied, and how I'd build the twelve weeks before a selection weekend. Written from my own application, free, no pitch.