What should never change, even as everything else does?

Many of our debates are about change: how fast, in which direction, who gains and who loses. We spend less time on the opposite question: what should we protect, whatever else shifts?

It might be a principle, such as equal treatment before the law. It might be a practice, a place, a language, a tradition, a standard of care, or a freedom. It might be a way of treating people that no technology or economic pressure should alter.

We are asking readers to name one thing they believe should stay the same over the next fifty years, and to defend it. A good answer would say what it is, why it matters, what threatens it, what would be lost if it changed, and what would count as a good reason to change it after all.

The best answers will take seriously the strongest argument against them, and will tell us whether the thing is worth protecting for its own sake or for what it makes possible.