I think it is trendy now to discount older sayings. The head heat loss stuff is significant. But it is not just the hat, it is loss from head and neck (think balaclava) and heat loss and inhaled cold from breathing. When I was seriously winter backpacking (-20 to -40)the minute we got to camp we stompped the tent platform, then immediately took off wet clothing and put on insulating clothes- parkas with tunnel fur lined hoods to pre-warm the air before breathing, insulated pants, Micky Mouse boots, big mits and a face mask. Then we melted water, cooked dinner, and went to bed. No sitting around socializing! When we got to our base camp, we spent an entire day building a huge snow cave that we lived in for more than a week. In the snow cave we could sit around and socialize since it was about 30 degrees inside. In fact we had to be careful not to get it too warm. We would light one little candle and it would be enough light. The snow cave was not an emergency shelter, but a planned structure. It was downright luxurious compared to tent camping.