Yesterday I had the singularly unpleasant experience of firing* someone who doesn't have most of the attributes you'd associate with a fire-ee. She wasn't incompetent, she wasn't unpleasant. She worked hard and was diligent and showed up. She was professional and intelligent. And yet I found myself explaining to her that we were parting ways.
The reason for the parting is both painfully simple and deceptively complex. The simple reason is that her client did not view her as adding value to their organization. In consulting we call this a "bad fit", and they happen despite our best efforts. I'm proud that we went five years before one happened, but when one does happen you have to deal with it quickly and carefully.
Since we value our clients, we refunded an entire month's worth of fees for the consultant in question and have been working to identify her replacement. The client understands the situation and is appreciative of our efforts, so we have that half under control. However, we then have a consultant without a client. In many organizations, this is a no-brainer: you send the consultant on their merry way and call them back if you need them again in the future. In ours, however, this is a bigger issue: our consultants are all salaried employees, and if the consultant possesses all the basic skills and a client-oriented desire to succeed, we'll work to find a new engagement that is a better fit.
The more complex reason for the parting is this: it was clear that the person did not enjoy life as a consultant, and that the demands placed upon her were making her miserable. Unfortunately, those demands are typical of our field, and so after a brief discussion we agreed that it was best to part ways. She made it easy by understanding the reality of the situation; I would have had a tougher time if the person had stubbornly clung to the idea that this would work out.
* I refuse to use sanitized terms like laid off, let go, or (my personal favorite for being disingenuous) "transitioned out of the firm." If I'm telling you you're not allowed to come to work tomorrow, you're fired, even if it's not because of negative performance issues.