There may be no etymological connection between thesis and Theseus, but there is a metaphoric one. Theseus, a mythical hero of ancient Greece, found his way through the Cretan Labyrinth by following a thread. Likewise, a thesis allows both a reader and writer to find their ways through a labyrinth of ideas by following a thread of thought. This thread begins with what the reader and writer already know, and leads them to the destination you have in mind.

That is, a thesis crystallizes the controlling idea of an essay and, thus, helps us to keep track of that idea as it develops through the body of the text.

If we were not able to formulate theses and to understand and evaluate the theses of others, we would be hopelessly lost amidst a maze of chaotic impressions, for there is no structure to experience except that which is imposed by the human mind.

To provide that clear and guiding thread, you must clearly define where you want your readers to end up. A focus sheet is helpful in clarifying purpose and audience. Once you know what effect you want your work to have on your readers, you can determine what they they already know and what they need to know in order to reach your goal.