“Overenthusiasm kills bodybuilding progress. It’s the most elementary error, but everyone seems to make it. A young bodybuilder begins training to build up his physique, performing five or six total sets for each muscle group, and soon he notices lumps of muscle appearing all over his body. ‘Wow! This is really great,’ he thinks. ‘If five sets is working this quickly for me, then 10 sets has to work twice as well.’ So, the next time in the gym he ups the number of sets he’s doing for each body part. For a week or two, he continues to make considerable muscle gains, but his progress soon shudders to a halt. 

Don’t Cross the Line

This anecdote illustrates one of the most crucial, but overlooked, axioms in bodybuilding: More isn’t necessarily better. There’s a fine dividing line between doing an optimum amount of training and doing so much that you become overtrained. And this line is easily crossed.”

Joe Weider, from Competitive Bodybuilding by Joe Weider with Bill Reynolds

Joe Weider helped keep champions like Arnold Schwarzenegger from overtraining, ensuring their progress.