A big factor that separates those who achieve modest gains from those who make impressive gains is the level of weight training intensity.
To stimulate the muscle fibers to grow bigger and reach their fullest potential, you must take every set you perform the point of muscular failure.

Muscular Failure: Is the point at which no further repetitions can be completed using proper form.

Sub-maximal training intensity will leave you with sub-maximal results, plain and simple.