Final answer:
The incorrect statement about thesis statements is that they should begin with the infinitive form; instead, they should be declarative, focused on one key idea, and provide a brief preview of the essay's content.
Step-by-step explanation:
The statement that is not true about an effective thesis statement is that it should 'Begin with infinitive form.' An effective thesis statement does not necessarily start with an infinitive (to do something), but rather should be a declarative sentence that clearly states the main argument of the essay. It should encapsulate the central idea, be focused on one key idea, and offer a brief preview of what the rest of the paper will support. Essentially, a good thesis statement establishes the topic, takes a position, and outlines the reasoning that will be elaborated upon in the work.