Valence effect

The valence effect of prediction is the tendency for people to simply overestimate the likelihood of good things happening rather than bad things. ("Valence" refers to the positive or negative emotional charge something has.)

This finding has been corroborated by dozens of studies. In one straightforward experiment, all other things being equal, participants assigned a higher probability to picking a card that had a smiling face on its reverse side than one which had a frowning face.

In addition, some have reported a valence effect in attribution when we overpredict the likelihood of positive events happening to ourselves relative to others. See self-serving bias.

The outcome of valence effects may be called wishful thinking.