I think once they have tried a few routines that have been written by other people and found out what works for them.
Also once they understand they have to do legs and not just curl themselves in to oblivion all the time.
At the end of the day every routine was trial and error originally, but i think to design your own (or someone elses) then you have to understand WHY they were trialed and WHY the error occured, otherwise you are just gonna end up spinning your wheels.
TEAM CROM (supporter) !!!!