i believe threads like this can be invaluable, and not just for the novice hiker either. Reading accounts of real world experience can save lives. So here goes my experience...
Ive noticed most of these posts involve rain or snow....Interestingly enough mine doesn't involve either. It involves heavy fog.
My girlfriend and I were section hiking Virginia last year, Early October. We were just north of Grayson Highlands hiking sobo. The previous day was quite warm, warm enough to sweat and even got a little sun burnt. In fact I remember walking around camp without a shirt on that evening. It rained that night dropping the temps significantly. The rain had ceased at some point overnight but it left the air completely saturated. We packed up camp, had warm coffee and a bar and starting hiking.
I was hiking in what I had on the day before which was shorts and short sleeves; although we had our "winter gear" with us. About 2 miles in I noticed I was shivering. I thought if we just kept moving I would be fine. My girlfriend has many more layers on that I and was fine but noticed my shivering. I was being stubborn and insisted I was fine and to just keep moving thinking I would warm up and the temps would rise, especially given the warm temps the day before. 20 minutes later the shivering hadnt stopped and I noticed I was feeling a little "slow" in my head. The girlfriend finally convinced me to stop being an idiot and put a layer on. I complied, warmed up and felt much better.
Moral of the story, dont be stubborn and be preemptive. Dont wait until the shivering starts. Be one step head. On my JMT thru hike this August I always took the approach of "I would always rather have the extra layers on and be too warm than to try and put the layers on to warm up"