This follows immediately from the idea that People Are The Key To Success, which says that you should always hire the best engineers. This principle says that you are better off allocating just a few good, experienced engineers on a critical task than to put many inexperienced engineers on it. This is Don Reifer's "Management Principle #6." On the other hand, Manny Lehman warns that you can't rely too much on "a few good people"; what if they quit? The best advice is to have the right mix of people on a project and take care not to gravitate towards either extreme. Those people with the most experience are probably closest to retirement. Keep them working with people with less experience so their knowledge isn't lost in the future.
Reference:
Reifer, D., "The Nature of Software Management: A Primer," Tutorial: Software Management, Washington, DC: IEEE Computer Society Press, 1986.
