My experience confirms the general concept here (the number at 5% is arbitrary I'd place it higher than that). The point is (and I have found this to be true) if you deal with enough people you will hit on people who have let's say issues and do not think clearly or even close to rationally and there is simply no pleasing them. So for business the idea that you need all of your customers to be happy is simply not going to work. That is what I have found in actual practice over many many years.

Separate point when you are starting out in some business the easiest and first customers you get are the ones that nobody else wants or gives bad service to because they are irrational and unreasonable. (Keep that point in mind..)

There is an example with Zappos of someone being able to spend an entire day pleasing one customer. That is entirely unreasonable and except for the story and publicity value of that event makes no sense at all since anyone who wants to spend that much of your time is not going to be a customer that you (probably) want long term. At a certain point you simply have to (in business or life) walk away.

https://www.refinery29.com/en-us/2016/07/118020/zappos-custo...