Training is perhaps the most important part of professional development, yet in almost all organizations its value is substantially overlooked.

This is understandable on the surface. The common reason training isn't a big part of career development and human resources is a concept I call "fake intellectual theft"--managers are afraid they'll spend their scarce budgets on very expensive and often quite specialized training for their direct reports, only to watch them carry all that knowledge directly to another organization, probably for more money. The natural reaction to the learn-and-leave effect--which honestly does happen, but not to the extent that is feared by most managers--is to stop investing in training.

Analysis:

This is shortsighted. It tells your good employees you don't care about their development and don't trust their career ambitions, which all but pushes them out the door at their first realistic opportunity. Your less-good (to put it politely) employees are the ones who end up staying, and of course they'll be at that same mediocre level of proficiency because, well, you've already decided not to train them. You've doomed yourself to an average team, at least until you decide to shake things up.

Don't Promote People Beyond Their Competence.