Once upon a time, there was a small town. There lived a man by himself who couldn't see. He was blind. Yet, he carried a lighted lamp with him whenever he went out at night. One night as he was coming home after having a dinner outside, he came across a group of young travellers. They saw that he was blind, yet carrying a lighted lamp. They started passing comments on him and made a fun of him. One of them asked him, "Hey man! you are blind and can't see anything! why do you carry the lamp then?!"The blind man replied, "Yes, unfortunately, I am blind and I can't see anything but a lighted lamp which I am carrying is for the people like you who can see. you may not see the blind man coming and end up pushing me. that is why I carry a lighted lamp". The group of travellers felt ashamed and apologized for their behaviour. 
We should think before judging others. Always be polite and learn to see things from others point of view. 