This assumed truism is actually arguable.

I can see that some furniture is better than others, but I actually am rarely all that uncomfortable regardless of the furniture. I will sit on a hard stool or a cheap chair with compressed dead cushion or a sumptuous stuffed chair almost equally fine all day long doing something engaging. As a kid I spent all day every day on rock hard absolutely non customizable chairs, and was fine. Because I was a kid.

The argument that you are the major ingredient in the equation of your comfort, not the chair, holds up.