Much of life does not progress linearly or even continuously. Business planning requires that business people make assumptions. Some of those assumptions are good, but most are probably not. The question is what one will do to cope when your assumptions go bad.

Some failed assumptions you can shift with, others are fatal.

Spotify has made the assumption that people won't flock away from facebrick. There are all sorts of events that can kill social networks, and they're betting against that happening.