The difference between an instinctive reaction and a conscious thought is seen between:
1) Verbally lashing out at someone in a reactive fit of anger or rage and
2) Consciously saying to yourself, "I have so much anger towards them within me, I really want to yell at this person right now."
One is reactive and the other is a conscious thought.
Consciousness is where freedom begins because rather than allowing our impulses to govern our decisions, consciousness allows us to take a step back within ourselves to engage and become intimate with the impulses, desires, and underlying emotions that we find within us.
The enneagram calls this practice internal awareness. Self-help and business books call it self-awareness. What’s important is not what we call it, but that we practice regularly becoming present within ourselves and consciously inquiring how our emotions are affecting us.
The practice of self-awareness alone won’t cure a strong compulsive habit, but it is the starting point of transformation because you can't seek to change what you do not first see and understand.