Look at the opening sentences in the paragraph with the colored shading (see “Understand What Illustration Is”).

What is the strongest predictor of your health? It may not be your income or age but rather your literacy.

In this case, the topic — the strongest predictor of your health — is in the opening sentence, which is followed by a surprising main point: that literacy might be a predictor of health. Because the point is surprising, the reader will be interested in reading on to find out how it could be true. The writer demonstrates the main point by giving examples.

Often, a thesis statement in illustration includes the topic and your main point.