The basic key to their findings whether the event matches expectations. What is more, the expectation of an event matching your expectation alters your level of happiness in anticipation of the event itself… that is, until you actually experience it. It’s in the anticipation of an event that happiness itself often lives. This is because dopamine — a neurotransmitter in the brain correlated with positive feelings, among many other things — spikes in anticipation of a positive event, and then decreases during the event itself.

—Beau Lotto, Deviate, Weidenfeld & Nicolson, 2018

(Trata-se de um estudo do University College London, sobre a previsão se alguém se vai sentir feliz ou não numa determinada situação.)