The Carrot and Stick: The Forces of Evolution

The brain has a big stack of carrots and sticks, neurochemicals that make you feel good to reward you. We evolved these chemicals to prompt us to behave in ways that enhance our reproductive success. If your dopamine is chronically high, then your brain starts to close off dopamine receptors to compensate. You can go through a life dominated by the carrot chemicals or the stick chemicals; they're all in there all the time.