There is a real difference between consciously deciding to achieve a goal and actually controlling your behavior. Conscious decisions alone are often insufficient because underlying subconscious processes heavily influence what we end up doing.
For instance, deciding firmly not to eat something sweet, and then finding yourself eating it anyway, reveals an immediate conflict between conscious intention and automatic underlying behavior.
"Conscious decision is the intention; subconscious behavior is the execution."
Inspired by thoughts on self-regulation ("How to Outsmart Yourself" / TTC).