My former colleague, Boris Groysberg, has a new book out titled, "Chasing Stars:
The Myth of Talent and the Portability of Performance." Groysberg's work over the years has examined what occurs when "star performers" are hired away by another firm. His work shows that, in many cases, those stars experience a performance decline in their new organization. Why? Many reasons exist for that drop-off. Groysberg focuses on the notion that, often, exceptional performance is a function of not just the individual's capability, but also the support structure in their previous organization. What talent surrounded them? What systems supported them? What culture enabled their high performance?
Other reasons exist for this drop-off as well. For instance, sometimes star performers fall in love with the way they did their work at their prior organization so much so that they try to replicate that approach exactly in their new firm. They don't recognize the need to adapt certain practices and approaches to the new culture and context.
One might jump to the conclusion that home-grown talent is the way to go, given Groysberg's findings. One note of caution though... these same reasons for star performer drop-off can pertain to internal promotions as well. People can move from one team or one unit of an organization to another and experience the same type of decline for the same reasons cited above.