Working with what is already there can be an extremely powerful principle when instructing people. A math teacher used this principle to help a student who had to do a math re-examination. The teacher asked the student to make a list A consisting of topics that he already understood and a list B of topics which he did not yet understand. When both list were finished the teacher complimented the student with the result: "Wow, there are already many things you understand. Excellent!” Then, he asked: “Which is the first of the topics on the B list you would like to move to the A list? The student chose a topic from list B. The teacher asked: “Okay, let's start with that topic. I don't waste your time so before I started explaining things that you may already understand I'd like to ask you what you already understand about this topic.” The student explained what he already understood about it and what he did not yet understand about it. Then, the teacher explained the part he did not yet understand. This process was repeated with every topic on the B list. Every time when a new topic was discussed the teacher asked what the student already understood. By doing this, the student realized that he already understood parts of many topics of the B list and his self-confidence grew. Another advantage was that they could use the time very efficiently. No time was wasted on things that were already clear to the student. Topic after topic was mastered by the student with the help of the teacher. The student passed gloriously for his exam.