I'm a firm believer in the theory that people only do their best at things they truly enjoy. It is difficult to excel at something you don't enjoy.
Recently I met with a client who recruited a new team member with a view to this person being a potential successor. What appeared to be a great "marriage" has thus far proved to be a disappointment for all concerned. There are many reasons for this but it highlights why a successful marriage (whether to a prince or to an organisation) requires a bit more forethought and attention than the fairytales would suggest.