I admit it. I got a little cocky. I've been running a comfortable 5 and 6 mile loop for the last month or so, and thought my feet were reasonably well seasoned. In fact I was thinking that each year the spring re-hardening of the feet has gotten quicker and quicker. I forgot about the sun. Today was the first really nice day we've had in a while, with bright sun all day and temps up to the low 70's (F) I thought I'd have a lovely easy run of 6 miles on my favourite pavement trail. Within a couple miles I was aware that my feet were more than usually sensitive to the intemittant gravel on the trail and thought it was left over from the heavy rains we got last week. (Almost 5 inches in one evening.) The feet got unhappier every mile and I just couldn't understand it. Finally the penny dropped! They were cooking, slowly but sorely. I also managed to step on 2 puncturing object whose identity I couldn't figure. End result - I walked the last couple hundred yards home (first time ever) and am still wincing as I walk. I'll let you know how they recover overnight.