Emotional bias

An emotional bias is a distortion in cognition and decision making due to emotional factors.

That is, a person will be usually inclined
 * to believe something that has a positive emotional effect, that gives a pleasant feeling, even if there is evidence to the contrary.
 * to be reluctant to accept hard facts that are unpleasant and gives mental suffering.

Those factors can be either individual and self-centered, or linked to interpersonal relationship or to group influence.

The effects of emotional biases
Its effects can be similar to those of a cognitive bias, it can even be considered as a subcategory of such biases. The specificity is that the cause lies in one's desires or fears, which divert the attention of the person, more than in one's reasoning.

Neuroscience experiments have shown how emotions and cognition, which are present in different areas of the human brain, interfere between each other in the decision making process, resulting often on a primacy of emotions over reasoning

This might explain some irrational and damaging reactions and moves that might take place when those emotions are biased (in case of over-optimism or over-pessimism for example).