Within the past decade I was the beneficiary of a great kindness offered by a truly authentic person--Donna Blakemore. I was looking to transition into university fundraising as a career change. Donna saw my potential and took a chance on me (and I on her). For that, I am eternally grateful.
There's the heart of it--risk. Mentors take risks on mentees and vice-versa. It's a symbiotic relationship entered into freely without any guarantee of success. Each person becomes invested in the other. Time, energy, effort. The mentor is rewarded with the satisfaction of watching a protege advance. The mentee advances--albeit, haltingly at times.
If you've ever been on the receiving end of the magnanimous investment of a mentor, I recommend you consider mentoring someone else. It's the golden rule in action.