A thesis is a phrase that offers a concise summary of the main point or claim of a text. It usually appears in the introduction. In academic writing, the thesis often takes the form of a theory or claim that is going to be tested or proved.
On It Was On Fire When I Lay Down On It, Robert Fulghum tells stories of people who have put themselves in absurd situations. The thesis of this work is most likely something along the lines of: All humans have the capacity to end up in absurd, silly situations or There is something silly in everyone's character, even if it is not always apparent.