People in a positive mood such as happiness were shown under experimental conditions to have relatively unreliable memories, and show poorer judgement and critical thinking skills.
By contrast, those who experienced a negative mood such as sadness were shown to provide more reliable eyewitnesses accounts and exercise superior thinking and communication skills.
But could this be a case of reversed cause and effect? Maybe some people are happy because they have bad memories, poor judgement, and impaired critical thinking. This could lead them to wrongly evaluate their life as being much better than it really is. Every time they wake up in the gutter covered in drool, they may conclude that their exciting career in midnight outdoor dentistry must really be taking off.