increases the production of melatonin in the brain. This is how I balance my circadian rhythm and feel more rested during waking hours.
It's not an unbreakable rule. I always have a glass of water by my bed, in case I wake up parched, especially when I'm traveling. I try to follow this in order to be at my best, but if I need to pull an all-nighter or jump online with the development team, then I'll drink coffee. There's a level of flexibility and forgiveness with it. We need a lower resting heart rate to get into those deep levels of sleep, and cooler temperatures are one way to get there.