The following excerpt is from an essay called “Optimism.” It was published in 1903 and was written by Helen Keller when she was 23 years old. I think it speaks for itself, but I also think it makes the point that optimism is both optimal and essential. It's a powerful tool for living a productive life. If you like what you read here you can find the complete essay by clicking here: optimism-by-helen.
Most people measure their happiness in terms of physical pleasure and material possession. Lacking this gift or that circumstance, they would be miserable. If happiness is so to be measured, I, who cannot hear or see, have every reason to sit in a corner with folded hands and weep. If I am happy in spite of my deprivations, if my happiness is so deep that it is a faith, so thoughtful that it becomes a philosophy of life,—if, in short, I am an optimist, my testimony to the creed of optimism is worthy of hearing. As sinners stand up in meeting and confess to the goodness of God, so one who is called afflicted may rise up in gladness of conviction and testify to the goodness of life. I long to accomplish a great and noble task: but it is my chief duty and joy to accomplish humble tasks as though they were great and noble.