Apple tree

Here is an analogy. It can be about politics (the right or left) or any other polar opposition like siding with one guy/opinion instead of another.

Take a tree with speaking green and red apples. You eat a red apple and like it. Then you prefer red apples above green ones. 

The speaking red apples prefer their own. They say that green apples taste bad and point out a rotten green apple for you to eat. The taste of this apple sickens you. The red apples never point out the good green ones. Well, maybe sometimes.

The rotten red apples are kept from you to eat by the red apples. 

In the end you have been fooled by your own taste and the red apples who say that the green apples are rotten to the core. Only a red apple is good.

Reality: Exactly how many red and green apples are good or rotten is covered by a veil of self-delusion and deceit. 

Facing up to your own biases is probably the hardest thing in life. 

Maybe if you can stand back and look from a distance you can count the apples, red and green and see which are tasty or rotten. 

But you have to stand back without tasting the apples.