It's all mental. Well a few Wim Hoff breathes and then the rest is in the head. After a bit your body gets used to it. It's nice to have that other side of you take control and say 'NO I'm not staying comfortable! '
Start with 15 seconds at the end of your normal shower. Stay there for a week, then move up to 30 seconds.
It's really great for your cardiovascular system and makes you feel alive!!!