i mean realistically speaking

It is basically like an ancient form of vaccination against poisoning. (poisoning was a pretty common way to assassinate nobles) Although they had people who taste test their food, slow poison can't be detected by taste. So noblity (especially royalty) often had to drink small doses of poison from a young age to build up resistance. There were also 'endurance' trainings which is similar to what the name suggests except it is traumatizing and can cause death.