" Once we get the anticipated reward, brain dopamine firing increases well above tonic baseline, but if the reward we anticipated doesn't materialise, dopamine levels fall well below baseline. Which is to say, if we get the expected reward, we get an even bigger spike, if we don't get the expected reward, we experience an even bigger plunge.
We've all experienced the letdown of unmet expectations. An expected reward that failed to materialise is worse than a reward that was never anticipated in the first place.
How does cue-induced craving translate to our pleasure-pain balance? The balance tips to the side of pleasure, a dopamine mini spike, in anticipation of future reward. Immediately followed by a tip to the side of pain, a dopamine mini defecit, in the aftermath of the cue. The dopamine defecit is craving and drives drug seeking behaviour. "

― Anna Lembke , Dopamine Nation: Finding Balance in the Age of Indulgence