Love and hate falsify our judgment entirely. In our enemies we see nothing but faults—in our loved ones nothing but excellences, and even their faults appear to us amiable.
Our interest, of whatever kind it may be, exercises a like secret power over our judgment; what is in conformity with it at once seems to us fair, just, and reasonable; what runs contrary to it presents itself to us, in perfect seriousness, as unjust and outrageous, or injudicious and absurd. Hence so many prejudices of position, profession, nationality, sect, and religion. A conceived hypothesis gives us lynx-eyes for all that confirms it, and makes us blind to all that contradicts it. What is opposed to our party, our plan, our wish, our hope, we often cannot comprehend and grasp at all, while it is clear to every one else; but what is favourable to these, on the other hand, strikes our eye from afar. What the heart opposes the head will not admit. We firmly retain many errors all through life, and take care never to examine their ground, merely from a fear, of which we ourselves are conscious, that we might make the discovery that we had so long believed and so often asserted what is false.
Arthur Shoppenhauer | The World as Will and Representation.