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 some entity possesses.

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.