The words “optimism” and “the left” do not seem to go together very well these days. The dominant view on the left--reinforced by the election of Donald Trump--is as follows: (1) progress in today’s world has largely stopped and in many ways reversed; (2) the left is weak and at the mercy of a rapacious capitalism and a marauding right; and (3) the outlook for the future is bleak, with ordinary citizens suffering even more deprivation and the planet itself sliding inexorably toward catastrophe.But all these propositions are wrong. It is not the case that progress has stopped. Today, we live in a freer, more democratic, less violent and more prosperous world than we ever have before.It is not the case that the left is at the mercy of the right. The form of the left is changing but its numbers are strong and growing. It remains a vital force—the vital force--for reforming capitalism.And it is not the case that the future of humanity is bleak. The problems we face today are solvable and, moreover, are likely to be solved in the coming decades. Life for ordinary citizens should improve dramatically over the course of the 21st century.It is not just that these pessimistic propositions are wrong. They also do real harm to the left by undermining its appeal. Pessimism makes people less likely to believe in positive change, not more likely. It is time for the left to realize that their romance with pessimism is a bug not a feature of their current practice. There is no substitute for optimism and an economic climate that promotes optimism. The time has come for the optimistic leftist.