"Fundamentally, a destructive emotion - which is also referred to as an 'obscuring' or 'afflictive' mental factor - is something that prevents the mind from ascertaining reality as it is. With a destructive emotion, there will always be a gap between the way things appear and the way things are.
"Excessive attachment - desire, for instance - will not let us see a balance between the pleasant and the unpleasant, constructive and destructive, qualities in something or someone, and causes us to see it for a while as being one hundred percent attractive - and therefore makes us want it. Aversion will blind us to some positive qualities of the object, making us one hundred percent negative toward that object, wishing to repel, destroy, or run away from it.
"Such emotional states impair one's jugdment, the ability to make a correct assessment of the nature of things. That is why we say it's obscuring: It obscures the way things are.[...]"
Destructive Emotions, by Daniel Goleman