READ: How to Write a Killer Thesis Statement

A thesis is the result of a lengthy thinking process. Formulating a thesis is not the first thing you do after reading an essay assignment. Before you develop an argument on any topic, you have to collect and organize evidence, look for possible relationships between known facts (such as surprising contrasts or similarities), and think about the significance of these relationships. Once you do this thinking, you will probably have a “working thesis,” a basic or main idea, an argument that you think you can support with evidence but that may need adjustment along the way.

http://writingcenter.unc.edu/handouts/thesis-statements/