"The optimist thinks this is the best of all possible worlds. The pessimist fears it is true." - J. Robert Oppenheimer.

J. Robert Oppenheimer was a brilliant physicist of his time, ultimately proving vital to the construction of the first atomic bombs.

Julius Robert Oppenheimer was one of the great American physicists of his time. Working with Albert Einstein, Oppenheimer was one of the leading researchers of the Manhattan Project, and was instrumental in the development of the first atomic bomb. After the detonation of the first nuclear weapon, he regretted everything he had contributed to the project, knowing that he had just created a true "weapon of mass destruction". 

This quote holds amazing complexity and depth while maintaining a beautiful simplicity. The first half, "The optimist thinks this is the best of all possible worlds" focuses on the good in life, shares a view that has faith in the nature of us humans, and hopes that in all of our advancements we have come to make this world the best place that it could possibly be. This outlook is heartening, but is optimistic to the point of naivety. However, the second half, "The pessimist fears it is true", lands on the other side of the spectrum. The second half brings to mind the considerable flaws in our world; the widespread of starvation and disease throughout Africa, or the thousands killed every year in wars motivated by cultural and political differences. The pessimist fears that the world we have created is as good as it could possibly get, because he knows that overall, it's not that good.