“Strength is the outcome of need.”—H. G. Wells 

While there are many reasons why a lot of lifters hit plateaus and fail to make progress (they've ceased or more realistically never started serious squatting; they still devote certain days to train certain body parts; they consume about a third of the protein they need; their intensity level is permanently stuck two clicks shy of lethargy), the most common cause remains their goals simply don't require it!