How the body and mind adjust to extreme cold.
Cold adaptation is both physiological and psychological. Your body learns to manage heat more efficiently, and your mind learns to accept cold as normal rather than uncomfortable.
Layering becomes second nature. You learn which fabrics work, how to cover exposed skin, and when to stay indoors. There's a whole knowledge system around cold weather that I had to learn from scratch.
The first winter was hard. By the second, I barely noticed the cold. That's adaptation.