Getting frostbite is a very real part of a protracted polar expedition. It’s only too easy to work a bit harder than you should, work up a sweat and then the sweat ices up on the inside of your jacket or gloves. You have to operate just under the sweat level (which in minus 40C is quite high). Secondly, it’s about experience. You need to know how long you can freeze your hands for as you fix a broken ski binding, for example, before you have to stop what you are doing and devote some attention to warming up your hands. You can only know how far to push your body before doing damage to it if you have been in the field and have the experience. Lastly, it is genetics. Pure and simple. Some people are just better in the cold than others.