Good thread on firing people. One of the best nonobvious pieces of advice I've heard about this topic: If you never fire people then you can't build an A+ team because no hiring process is perfect.

Great thread. The other common reason I've seen is "this person is not amazing, but pretty good, and maybe that's good enough? Let's wait a few more months and reassess later." (A few months later: "damn, should have trusted my gut earlier on them not being amazing.")