Principles are ways of successfully dealing with reality to get what you want out of life.
Ray Dalio, one of the world’s most successful investors and entrepreneurs, cites principles as his key to success.
It is very difficult to fire people you care about. Cutting someone that you have a meaningful relationship with but who isn't an A player in their job is difficult because ending good relationships is hard, but it is necessary for the long-term excellence of the company. You may have a need for the work they're doing (even if it's not excellent) and find it hard to make a change. But they will pollute the environment and fail you when you really need them.
Doing this is one of those difficult, necessary things. The best way to do it is to "love the people you shoot"--do it with consideration and in a way that helps them.