It often comes from one of two kinds of people:
People who give themselves feedback in the same heartless tone. They don’t hesitate to brutally lash out, because that’s the noise they often hear inside.
And folks who honestly believe that their work is flawless. They can’t understand how anyone else can fail to measure up, because they never seem to.
Of course, each group has a significant (though different) problem. In fact, now that they’re spreading their harshness with others, they have two problems.
When in doubt, look for the fear.
In my experience - this is so true. In the past, harsh feedback has told me more about the person giving the feedback, than about me.
I once had to provide a lot of evidence to an invigilator for a degree course. The evidence had to be specific and I needed three examples for each KPI. After some hours, when he'd gone through it all he turned to me and said - so, do you think you're the finished article?
Flabbergasted I was!