Salience
How much you like something determines how much your neural network is reinforced by a specific reward. The higher the salience, the more impact it has on your synaptic growth and the resulting probability that you will do whatever you did to get that reward again.
If you like something too much and don't practice moderation, you get addiction.
Relative salience and frequency of reinforcement can allow you to fully predict how often a subject will choose one option versus another, undermining any argument for free will. This is known as operant conditioning.
See Motivational Salience on Wikipedia.