I haven't done much winter hiking at all, but have turned back on three hikes that I can think of. Two of the three were on the MacIntyres. One on the way to Marcy (sort of...)
First one was with my cousin. It was winter, and we just started late from Marcy Dam. Actually we turned back because of laziness. Looking back, we had picked one of the longest routes to get to Marcy and couldn't even do that hike in the summer now. It was one of our first hikes in the High Peaks.
Second one was with my brother. We planned to do Wright and maybe Algonquin. Approaching the treeline on Wright (if my memory is correct...) we turned back because of two reasons. One, there was a lovely storm approaching. We could see it dumping snow a little south of us. Second, my brother was vomiting and couldn't keep food in his stomach. He was working on less than 1/2 hour of sleep in 24, having worked all night.
Last was this summer in August. Same cousin as the first one and my brother, on Wright again, planning on doing Algonquin and Iroquois. At the summit of Wright, we realized that my cousin had forgotten a shell, and had only a long sleeved cotton shirt on. Summit temp was in the low 50s high 40s, with a stiff wind and complete cloud cover. I loaned him a vest and wool hat to keep his body temp up, but had to bail on the remainder of the hike as he wasn't prepared for the possible summit conditions on the other 2 peaks.
If in the same situations again, I would turn back again every time.
To echo a previous sentiment, Mohammed had it right.
Later,
Josh
P.S. In response to the headlamp sub-thread here. I bought a Black Diamond Ion, 2 LEDs, single 6 volt lithium battery. I have hiked at night with it, using a small titanium LED spotlight for long distance lighting when necessary. I agree it doesn't put out that much light, but have found it sufficient when supplemented minimally. The BD Moonlight has 5 LEDs and puts out much more light, sufficient alone in my opinion for night hiking. The best on in my gear closet is still the one I made, 3 red and 2 yellow LEDs. Look up the thread if you want to see pics. (Headamp, started by Bee.)