Why Songkran is important to the people who grew up with it, and what visitors miss?

Most writing aimed at travellers stops at the water, which is the most visible part and probably the least meaningful one. The parts involving family, elders and temples happen largely out of sight of anyone on a holiday, so visitors end up describing a festival they only saw half of. We are not going to explain somebody else's tradition back to them. The practical planning side is what we cover: https://meetlocale.com/guides/best-time-to-visit-thailand If you are Thai or have spent Songkran with a Thai family, what does the day actually involve that outsiders never see?