Two types of PFS

Why do some guys get PFS staight after starting fin, but some get it only after quitting?

Good question. Are the symptoms the same? Maybe the body is trying to adjust or compensate for the drug use. Almost a type of resistance as to where the drug actually becomes a stimulant that the body works against in some. Take away the drug lets say after 20 years or so and the body no longer has this stimulant to counteract. Hence crash, and maybe some dont even get this far. Idk.