Why do Liberals have an Optimistic View on Humanity?

-Liberals do see Humans as selfish, but they can control their Future, thus meaning Humans have an Optimistic View of Humanity. Society will Improve! -Rational Individuals realise Cooperation and Compromise is Better and more Sensible than War -This leads to Tolerance and Harmony in Society, as well as linking the Liberal Belief in the Value of Education, and human Capacity to Learn