[TulliusCicero]

I think it's that successful momentum can paper over internal business failures for a while, which means you lose a sort of natural selection where the worse employees -- and especially the worse managers -- would screw up in an obvious way and get booted out. And without that pressure around, people don't have to perform.

Basically, a company that's in an extremely strong position from prior successes may lose internal feedback loops that kept the people and culture on track.