Don't judge a book by its cover

Why do people judge others without even knowing them?

It's human nature- really it's in the nature of all social animals- to be judgmental, and, more to the point, to be able to judge others quickly.

In my humble opinion people think that they know everything. Basically they don't want to listen to your point of views. They already tend to have a notion about what should be the possibility seeing your conditions. There are many possibilities in life but eventually they are overlooked.

People try to put you in a box telling your boundaries and limitations. It takes hardly a minute to form an image of you in their minds which won’t change until something dramatic happens. So unfortunately they see your credentials, not your hidden talent. 

People always tend to see themselves as being better or placed higher on the pyramid than others. The only way to escape from the constant onslaught of negativity is to either escape the toxic environment or start looking at the judgemental people consciously, although the latter advice is more difficult to manage just because they manducate your precious energy away, hence it is wiser to just completely abstain from even engaging with people. Your time is precious, spend it with people that are of the right attitude and hold to higher moral principles. Be open to the light rather than the dark. Good luck!

“Don't judge a book by its cover” 
― George Eliot, The Mill on the Floss

“Never judge someone's character based on the words of another. Instead, study the motives behind the words of the person casting the bad judgment.” 
― Suzy Kassem, Rise Up and Salute the Sun: The Writings of Suzy Kassem