The sleeping bag (at least as I've understood it) works in that way, that it uses the heat the body creates to create a layer of heat air between the body and the sleeping bag's border, therefore providing pleasurable feeling of warmth.
But after watching some videos about people such as Wim Hof and scientific research on their body's behaviour, I've found that something quite opposite is taking place there. Their skin is getting very cold, while the body core remains hot. So, there's no pleasurable feeling of warmth, there's no warm air layer, the skin is feeling trembling cold, and the body protects itself from cold isolating the skin from the body core, therefore using skin as isolating layer.
So, when using sleeping bag, the body is not trained to develop such mechanism, because the skin has always contact with warm air, am I getting it right? So, actually, isn't using sleeping bags stopping the body from real accommodation to cold conditions?