Our brain is a prediction machine. It predicts the amount of suffering that is going to be caused by an external event. But it is bad at doing so! Usually, it overestimates the amount of suffering we are going to endure. The same is true with pleasure. The brain will overestimate the amount of pleasure that we are getting from an external event. Buddha realized this very well by suggesting that all forms of craving (including aversion or craving for non- existence) should be avoided.