I originally visited a podiatrist because I was suffering from chronic shin splints. He prescribed a set of custom-molded orthotics, which is a common recommendation for podiatrists to make. The problem was that the particualr orthotics he prescribed were drastically excessive and overbuit, the equivalent of huge, thick glasses for an only slightly nearsighted patient. They were the kind of orthotics that would normally be prescribed to an elderly person with real mobility problems, not an athletic young male suffering from a minor running injury. Wearing them was like walking around with my feet encased in slabs on concrete.
I wore these orthotics everywhere, both walking and running for five months before I wised up and realized that I wasn't getting better and that I was being led around by an idiot. At some point I became frustrated, tossed the orthotics away and tried running without them. Immediately after I resumed running "normally", I began experiencing crushing pain in the joints of my feet that didn't go away after I stopped. In the following weeks, I learned that this pain represented permanent damage to the cartialge in those joints and that I had caused permanently osteoarthritis in my feet.
As it turns out, the excessive support that the orthtoics provided had "shielded" the joints of my feet from the normal stress of ambulation, and as a consequence, the cartialge in those joints had atrophied, or become weak and vulnerable. Just as muscles become weak if you don't use them, joint cartilage becomes weak and soft when not exposed to the stress of normal weightbearing, and in this state, it is vulnerable to damaging stress. When I attempted to resume running noramlly, without the orthotics, the imposition of stress that had once been easily tolerable caused permanent damage to the weakened cartilage.