Satmya is a reason why a diet that works for one culture may not work for another.

When one is introduced to something unwholesome from a young age and becomes habituated to taking it, they can adapt and withstand the negative effects, but not completely.

If one's family have been taking an unwholesome substance or performing an unwholesome habitual action for generations (e.g. working late at night), they further become immune and compatible with that substance or action, but not completely.

If the unwholesome substance is indigenous to the land and climate that the person resides in, that again increases harmonious compatibility, but not completely.

Harmonious health is not completely maintained because it will can them inflict them later in life. When their immune system becomes weak or they approach vata age (60+).

For example:

There is a story of a king in India named Mahmud Shah, who lived in Gujarat in 1500 AD. He raised his son on tiny doses of poison to avoid threats of poisoning by his enemies. He was also said to chew different poisonous leaves and spit on whomever he wanted to kill. He was said to have 3000-4000 wives, and whenever he slept with one, she was found dead in the morning.