This one is the toughest:

The Early Hire: These are the people who begin working at a startup in its early days before the company knows what it will become. Over time, the business changes and suddenly that early hire does not quite fit in. It’s a tough situation for both parties but if the person is not the right fit anymore then it is even worse to put off the inevitable.

They're all tough.

I never understood this one:

The Failed Promotion: This is the person who delivered value in previous roles but in their new job they are just not cutting it. A sign of the problem: the new hire is getting up to speed faster than the person who received the promotion. The person, the new role and the point in time of the startup may all contribute to the poor fit. It’s a step backward for the person to go back to their old job. Let them go and they may find a better role with a new company that better fits their skill sets.

I never understood this one... I just don't see the logic of firing someone you were impressed enough with to promote in the first place. A situation like this requires mentorship, or at least a face-saving lateral move. It's like burning down a chocolate factory because your mixers can't handle brazil nuts.