What is the name of a book about a man who is on a journey with a pessimist and an optimist?

I read a piece of this story my freshman year of college for my literature cl. And I can't remember the author or name of the book. There is a man who is on a journey or something. He runs into two men. One always points out the bad that happens in every situation, no matter how good it may look at first. The other man always finds the good, no matter how bad the situation. Their point of view seems to be just let fate take over because no matter what it will be for the good/bad. In the end the man on the journey decides not to leave everything just to fate, that he must work for what he wants. There is a quote that sticks in my mind that goes something like the man decides he will "Till his own garden" or "Plow his own field" or something along those lines. Does anyone know what I'm talking about?