Picture: From cellanr – https://www.flickr.com/photos/rorycellan/21834269682/, CC BY-SA 2.0, Link
“Nothing has given me more mental confidence than Having the Ability to move direct from room temperature to the cold,” Dorsey says.” [E]especially in the morning, moving into an ice-cold tub from only being hot in bed is it just unlocks this thing in my mind and I feel like if I could will myself to do that thing that appears so small but hurts so much, I can do anything.”
From CNBC:

Twitter and Square CEO Jack Dorsey (42) walks 5 mph every day, eats only one meal a day, fasts all weekend, and attempts to meditate two hours every day. CNBC looked at 11 of the”wellness” customs, which he spoke on a recent episode of the Ben Greenfield Fitness podcast.