Mentors are people that are more experienced than we are and who guide us on our paths and help us to our goals. They help us use our own sources and less the sources of others. They are the people that help us be the best versions of ourselves.
This source comes into play less often but is still very important. It is especially helpful when you are trying to complete something or are struggling with somthing. You can look up to that person and seek advice. This souce can help you through hard times.