I was just eating some of my Valentine's Day candy and the infamous line from Forrest Gump came into my head: "Life is like a box of chocolates. You never know what you're gonna get."
Sometimes this happens with the matches you make in your mentoring programs. While the mentoring program manager will do his or her best to ensure the best possible matches are made--for both the mentor and mentoree's sake--the truth is you're still dealing with the unpredictability that is the human species. Some matches work out better than others. The program manager's main task is to recognize when a match isn't working...and to intervene and help get the match back on track. There are a variety of ways to do this--one-on-one conversations, group conversations with the match, providing resources to help the match, etc.
Unpredictability is okay--just as it was for Forrest and his life--it's knowing what to do during these situations that matters.