I have had a few occurances.Only 2 have persevered made it thru.Though one only does the upperbody exercises that i taught him despite persuading him to incorporate squats/deadlifts etc.The other one is about 80% as strong as i am, pround of him.
Most after a few sessions.
De-motivated, no self discipline or cannot endure the soreness the following day.1 or a combination of all factors.