Buddhist psychology describes four Mental Aggregates: Feeling, Discrimination, Primary Consciousnesses (5 senses and mental awareness) and the other aspects, gathered as the Compositional Factors.
The Feeling Aggregate is defined as ‘an omnipresent factor of the mind which labels experiences into three categories: pleasant, unpleasant or neutral’:
When the label of pleasant is given to an object, we develop attachment.
When the label of unpleasant is given to an object, we develop aversion, and sometimes even anger or hatred.
When the label of neutral is given to an object, we often don’t care about the object or even ignore it.
The process of labeling by the Feeling Aggregate usually only takes a fraction of a second. After applying the label, we tend to create a static opinion and image of the object in our mind. At this stage, the seed for prejudice is usually planted.
Once we have established the opinion that something is pleasant or unpleasant, we often need a large amount of evidence before we are willing to change our mind – that is, if we are prepared to change our mind at all. Once we labelled an object unpleasant or bad, it appears as if the object is all bad by itself, as if badness is an inherent quality. We may label a person “bad”, but the friends of this person would certainly not agree!
Therefore, we need to realize that “good” and “bad” are merely subjective opinions of our mind, and the opinion is often founded on nothing more than a first glance and an almost automatic label. Things and people change quicker than our labels! Everyone tends to prejudice. Labeling is a convenient way to quickly make some sense of our surrounding world by categorizing things in being “good” or “bad” to us. The main problem is that we tend to react to the world merely via these (over) simplified labels.
Read more on the subject at Source: Introduction to Emotions