Why was I so productive in Vietnam? Maybe and perhaps I prefer hot and humid climates?
Especially in todays world, in which air conditioning is cheap and abundant, if you seek the maximally productive and healthy life, perhaps hot and humid climates are best.
Moisture in the air, is good for your body. Also hot and bright is good.
Therefore perhaps the ideal locations for digital nomads include Vietnam (Saigon and Hanoi), Cambodia (Phnom Penh), and Thailand (Bangkok).