here's a direct quote from your buddy lyle mcdonald concerning progressive overload
"First off, I want to make the point that the primary stimulus for muscle growth is progressive tension overload; that is, you must subject a muscle to progressive overload (primarily in the form) of lifting more weight over time. This is discussed in more detail in Reps Per Set for Optimal Growth.
Other factors such as volume/fatigue/work (and frequency) are clearly important but, simply, if you’re not getting stronger (and here I’m assuming that you’re not changing your form to handle more weight) over time, along with providing sufficient calories and building blocks, you’re not growing.
Quick note: this doesn’t mean you have to add weight at every workout which is the HIT fallacy. Depending on your level of development, you might add weight every workout, you might stay at a given weight for 2-3 workouts or it might be 2-3 weeks before you can add weight in good form. But, if over some reasonable time frame, your training weights aren’t increasing, you won’t be growing."