While I think it's an organizational failure, even if folks aren't "growing" after 36 months, I definitely think there's institutional knowledge they have that helps them be more effective... the more time that elapses, the more of that institutional knowledge is lost and not documented.

Obviously it's not great to have companies hanging on by the thread of a single person's knowledge over 10 years, but I feel like at a lot of companies (especially smaller companies), this is the reality.