Predicting one's future emotional states in response to future events. It happens implicitly in most people.
However, I don’t actually think it works out because emotions have too many factors and still cannot be fully explained even in modern psychological research, so it can be wrong. Optimism bias, for many people, likely leads to disappointment in a non-ideal outcome, and pessimism bias reduces motivation for action. Rather, you can either detach from the outcome altogether because the world is too chaotic to be forecasted, and emotions are too unreliable as an affective forecaster. You can also try the Stoic practice of the premeditation of evil where you visualize the worst (which is different from pessimism).