Karl Moore and Devin Bigoness have a good column at Forbes.com about developing your people. They draw lessons from the development of National Football League quarterbacks. As they point out correctly, teams tend to take one of two contrasting approaches with their young quarterbacks. Some teams take the "immediate testing" approach - i.e. they throw them in the pond and challenge them to learn to swim. These quarterbacks often will struggle mightily in their rookie year. It's trial by fire. Other teams will adopt a "learning to win" model. These quarterbacks sit on the sidelines for some time, perhaps even several years, watching a veteran quarterback lead the team.
Each of these models has had its successes and failures. Aaron Rodgers succeeded using the "learn to win" approach. He spent four seasons as a back-up before becoming the starting quarterback for the Green Bay Packers. He went on to become a star and a Super Bowl champion. Peyton Manning, on the other hand, went the immediate testing route. His team lost many games during his first year, and he did throw many interceptions. However, we went on to craft a Hall of Fame career, won multiple MVP awards, and became a Super Bowl champion too. Of course, both models also have their share utter failures as well.
Moore and Bigoness do not advocate one model over another (appropriately, I might add). Instead, they propose that you should really understand your people, so that you can determine which model might be best for each individual. At the same time, you have to assess your organization's needs. You must balance what's best for individual against what is best for the firm. Some times, you might have to "rush" someone's development, despite some risks, because of a pressing organizational need. In other cases, you may determine that the organization can afford to give an individual a bit more time to "learn to win."
Importantly, if you do adopt at the "learn to win" model, you do need to still make sure that you present that individual with sufficient challenges and development opportunities. One risk, with this model is that a talented person will leave because they are not receiving the opportunity that they desire. In the NFL, teams have control over young players for several years. In companies, people can depart at any time. Thus, leaders must share their development strategy with the individual being groomed, and work with them to co-create a development plan that works for them and the organization.