My partner is a nurse by trade and has observed negligent behavior by medical professions every single time we've been to a hospital. Most of the time it is minor, but there have been times where she's had to speak up and get supervisors involved.

I'd say that "95% of people exhibit incompetence at least once per shift" is not far from the truth. I've been in taxis where the driver has run redlights. I built a house so I know all about keeping tradesman honest.

It's worse with lawyers, in that mistakes they make can go unnoticed for years or forever, so bad lawyers can still bring in lots of money to the company that provides them to you. Or so I think.

And the same with doctors, unfortunately, when they don't meet the person they treated again, when there's no follow up if it worked or not.

Plumbers, though, are different, in that then there's more feedback: does the water pipe still leak, or not? So they need to do something that actually works.

I think if we relax the statement a bit, to something like

"95% of all workers perform at the bare minimum required not to get fired or sued."

- it becomes quite defensible. To someone used to high performance, that does look like incompetence.

Also, it is much harder to fake it in typical trades than in "professions".