That's what I asked myself a few times after I picked up an injury earlier this year. Internet sleuthing led to the conclusion that it was some kind of tendonitis of the foot. Funny thing is I had been running a consistent 35-45 miles a week for about two months. Then one week I couldn't run much at all. Instead there was a lot of driving, especially of the slow, stop-and-go type, where you're constantly rocking the gas pedal and the brake with your foot. The next week I went for a run and by the time I got back I could feel a niggle under my driving foot. Sure enough, another run confirmed there was something wrong.
I ruled out a bunch of factors. There was no ramp-up in mileage. I'd been at a consistent 35-45 mpw for over two months. Running terrain was the same. Shoes were in decent condition. That pretty much narrowed it to the driving. In retrospect, the other thing that I neglected to do was stretching. Usually, I do. However, this time I didn't.
For the past couple of months, I've been babying the foot. Lots of rest, icing, and a bit of compression. Also bought a new pair of shoes and an arnica-based gel to apply. Cut down running. Restricted myself to around a 9 minute pace. Been doing some walking. All this seems to be helping. I've been able to get some decent running in for the last couple of weeks. Just have to take it slow and steady.
Frustration is the enemy and patience is the weapon in this game of recovery.