A mentor, our sages tell us, must be like an angel. That’s a problem. Having never seen an angel, you will always be in doubt: Perhaps the mentor you have chosen is not like an angel. How can you ever rely on your mentor while so unsure of his or her qualifications? So we will clarify: The mentor must be a human angel. An angel, because just as an angel has no body, no hatred, no jealousy, and is not in competition with you, so the mentor must remain objective and uninfluenced by any personal benefit from the advice. And yet...