You could write a similar article called 'The CEO Is Not Your Friend' or 'Your Boss Is Not Your Friend' -- whatever your relationship with someone, when they've got a job to do they're going to have to do it.

A couple of my angels are invite-to-the-wedding friends, but I still expect them to make rational decisions when it comes to their pro rata in later rounds, and I don't automatically expect them to invest in whatever I decide to do in the future.