Unfortunately, "fire fast" is now known widely enough to become a business fad / cargo cult. Which means, people are going to do it because it's the thing to do, and not because there's a good business reason to do it.
As a consequence, a company could strategically use "fire fast" by claiming it as a policy but not doing it. This would attract the people who perceive themselves as high performers, with minimal impact on employee morale.
This is true. Sometimes you have to let go of problem employees, but this should really be a last resort. Fire fast doesn't take into multiple considerations, such as the amount domain knowledge does this person possesses. If the person you want to get rid of has been there for 5 years, and knows certain systems in and out it may not be so easy to replace them.
Constant firing can also negatively affect your personal reputation. As a manager your job is to get people to succeed. Firing someone means that ultimately you failed in that. Sometimes this is unavoidable; there are times when people just aren't redeemable. Sometimes it's not. Good managers know the difference, but you have to remember that every time you let someone go for cause, that person probably didn't see it that way. That person has friends who work other places and all of them have a long memory. If word gets out that you quickly remove people who you can't seem to handle, people will want to stop working for you.
If the person you want to get rid of has been there for 5 years, and knows certain systems in and out it may not be so easy to replace them.
One of the biggest mistakes a company can make is keeping a toxic employee around because of their domain knowledge. The company I mentioned that I worked for for 9 years made that mistake. The employee had plenty of domain knowledge but was toxic, insubordinate, and displayed a poor work ethic. I know they had to be glad when that employee left on his own accord.
That employee was me. I look back on those days in horror.
I've only had a couple of longer term jobs, but at both employers, I noticed that the lowest level workers had a comprehensive oral history of every firing and interesting HR incident that had ever occurred, like an Icelandic saga. And of course it was told from their point of view. So you have to be aware that every firing will be remembered, you will never handle it perfectly, and you don't control the story. A firing has to be worth that price. That's a high bar.
I've learned a really, really bitter lesson in life about people. When I was about 23, I did have a good view of people although not supported with much data. Soon, I guessed that my view was wrong. Nope, I had been right. Net, after a lot struggle, I concluded, about people, in a nutshell:
There are a lot of seriously hurt, confused, uninformed, misinformed, damaged, hurting people out there who are so badly lost they are seriously constrained in what they can do.
Now, to be more clear, where they are constrained can be quite narrow and not broad. So, day in and day out, they can look fine. But for some real work in some well defined context, they can flop -- really be just unable to perform. Again, this can be tough to see without a lot of experience with them.
So, for firing, if you have a person who seems okay or even good in many ways but, still, somehow just can't do the job, with explanations, help, training, discussions, counseling, guidance, leadership, etc., then don't (A) be too surprised, (B) blame yourself or say that the fault is that of the organization, (C) conclude that you should try one more effort to fix the problem, (D) conclude that, of course, you should be able to fix the problem, etc.
Maybe reassign them to some work they can do, if can find that -- and sometimes it's possible.
Otherwise, just go ahead and conclude that they are unable to do the work, at least any of the work you have for them to do; don't be too surprised at this situation or conclusion; and let them go. Give them back to their families, the mental health community, the welfare system, or some such.
The big point is: Such broken people are surprisingly common.
For one level deeper, an explanation can be that their problems are not really cognitive or rational but emotional. And the main emotions can be fears, commonly from their being misinformed, uninformed, having had bad experiences, confused from what they have been through, etc.
I think that's reasonable, with the proviso that you could fire that employee with a tolerable effect on employee morale if you haven't already used up all of your "credits" on a policy of routine firings.
As a consequence, a company could strategically use "fire fast" by claiming it as a policy but not doing it. This would attract the people who perceive themselves as high performers, with minimal impact on employee morale.