personal anecdote; I spent a year barefoot as a teen after dropping out of high school. The only time I had anything on my feet was orthodontist visits they said i couldn’t go on without flip flops but nowhere else cared.

After about a year of this the callous on the bottom of my feet was so thick i could walk short distances on summer asphalt with zero pain and got a small square of windshield glass embedded in my foot and it just plucked right out and left a square hole, zero pain at all. The pads were about 3/4 cm thick at the ball of my foot and 1/2cm at the heel.

I did this after reading about this effect in a book and wanting to see if it was true and it really was!