Dopamine plays an important role in conditioning-based learning, especially reward-based conditioning
. When you are trained to recognize that certain behaviors bring about pleasant feelings for you, you can be sure that dopaminergic systems are operating.
As you start recognizing that when you do certain behaviors, you get more pleasure, your motivation will increase. This is how dopamine affects your motivation. You will be inclined to chase that pleasant feeling, which is governed by the dopaminergic system, over and over again.
Though this can be a good thing, when used unwisely, it can lead to your downfall. In a beneficial situation, the desire to chase dopamine may manifest as always exercising before going to work, as it leaves you with a refreshed and pleasant mood. But in an adverse situation, this same desire for dopamine may come about in the form of drug addiction, because you may derive pleasant feelings from the experience, and thus continue to chase that feeling by regularly increasing the dosage due to habituation.