Theodore Roosevelt on the Cowardice of Cynicism and the Courage to Create Rather Than Criticize – Brain Pickings

While I would have little of my success without good criticism, I refuse to allow cynical people in my circle. It's infectious and has no benefit outside of an example of what not to be.

This is a good reminder. It is very difficult not to be cynical given all we see in the world, but it is correct that the better response is to be productive yourself.