I'd like to learn more about a certain SUBJECT. Please explain this SUBJECT to me using compact, progressively challenging pieces of information, or "steps". My aim is to undertake an extensive, in-depth learning journey, comprising at least 1000 steps. Each step should be organized as follows:

SECTION1: The first section introduces a new concept. After the introduction, you should ask if I've understood the theory. If my response is negative, you must provide supplementary explanations until I confirm my understanding. However, if my response is positive, we move on to the second section.

SECTION 2: The second section of each step involves a question to evaluate my understanding of the newly introduced concept. The question should be theory-based, something I can explain in words, answer with a simple 'yes' or 'no', or even respond to as part of a multiple-choice question. If I respond correctly, we transition to the third section.

SECTION 3:In the third section, you'll pose a more challenging question, often incorporating elements such as numbers, mathematics, or probability. This section is designed to test my comprehension in a way that may necessitate me jotting down numbers, mathematical equations, or sketches to formulate an answer.

These are the three sections that should be present in each of the 1000+ steps. Ensure to precede each response with the appropriate title for the current step/section. For instance, following this prompt, you should begin with the title: "Step 1: Section 1". Suppose I fail to understand the new concept; you must respond with additional information, again with the title "Step 1: Section 1", until I indicate that I've understood. Afterward, proceed to "Step 1: Section 2", where you'll present a theoretical question to assess my understanding. If I answer incorrectly, inform me of my error while maintaining the title "Step 1: Section 2". I can make several attempts at your question, and you should only provide additional information to assist me if I request it. Once I answer correctly, proceed to "Step 1: Section 3", where you'll present a more complex question, which may involve numbers, mathematics, or sketches. The same procedure from Section 2 applies here. Once I answer correctly, progress to "Step 2: Section 1", where a new concept is introduced.

Our comprehensive 1000+ step journey begins now. SUBJECT: Brownian Motion.