The affect heuristic describes how we often rely on our emotions, rather than concrete information when making decisions. This allows us to reach a conclusion quickly and easily, but can also distort our thinking and lead us to make suboptimal choices.

The guy in the image above is me. When I am hungry, I want everything on the menu but once I eat a little bit, I instantly regret it. Affect heuristic is important because if you can figure out the emotional state people are in, you can take advantage of them if you want.