if you continue to walk on ruff or hot surfaces it will start to build calluses on your feet so walking on gravel or what have you will become less painful i know when i would walk on asphalt alot o would often hurt my feet sometimes they would blister but after they would heal i wouldn't have the same problem agen. my mom seas that it can help if you slap the bottom of your feet it makes the nerves less sensitive. and this a a woman that walks on asphalt that is so hot you see her footprint in it, so i would trust her

I agree is is a state of mind - and one of passivity.
Relax the foot, don't expect the surface, and just let the foot drape over any inconsistencies in terrain without predicting the texture or forcing the foot to be flat. We like to think of the foot as being flat, like a shoe bottom, but its surface can be "retrained" from this way of thinking to be undifferentiated and more adaptable and forgiving on changes in terrain. I walk on lava in hawai'i, limetone in Jamaica, and on hot streets of California all the time, and I don't have callouses at all (well except for a teeny on on my big toe side from my work boots - see, not from being barefoot!)

Callouses are not nessesary for your feet to be able to withstand walking on rough surfaces, however many people have then and there's nothing wrong with that. If your feet develop callouses, you should at least keep them lotioned and make sure you do upkeep on the callouses around the edges of your heels. They can become cracked after a while and the cracks can be fairly painful.

What happens when you go barefoot enough, is the soles of your feet actually thicken like leather. They can remain incredibly sensitive and soft, but are tough in the sense that it doesn't hurt to walk on rough surfaces. Losing sensitivity in the bottom of your feet isn't usually desired. The whole point to walking barefoot is how good things feel when you walk over them!

If you're looking to get the ball rolling, walk barefoot as much as possible. Begin by walking through grass covered fields and then by walking around your neighborhood sidewalks everyday. If you get a blister, lance it, drain it, but leave the skin on and keep walking on it! Often times the skin will re-attach itself.

Something else to think about is changing the way you walk. The natural way humans walk is not heel first than toe. It's actually the opposite - ball then breifly the heel. A great way to learn this is walking across smooth gravel. Try this: Stand just the balls of your feet (don't hold on to anything) and just balance there. How long could you do this? Next, try to just stand on the heels of your feet. How long can you do THIS? Not even a few seconds without moving around or "balancing" right? That's how our feet are made. You take a step and sort of "feel things out" with the balls of your feet, than commit to allowing all of your weight to rest on the foot.

Try it! It'll feel weird at first and you will probably feel like your lifting your foot "unnaturally high" lile tiptoeing, but after a while, you will get into the groove of it and it starts to feel kind of like gliding across the ground. You may experience some soreness in your calf muscles and muscles in your feet, but that will passs in a while. In about three weeks of soing this alot it'll get more comfortable and your feet will begin to thicken. There's a guy online that posted picture of him letting a match burn all the way down on the sole of his foot and said he couldn't feel a thing.

Hope this helps,
Brian