Before constructing the answer, it's usually good to clarify the problem. First, it's probably good to re-frame it in terms of past and present, not the (unknown) future. For example, assuming there were an extinct civilization 100,000 years ago which managed to pass that one sentence on, what bit of wisdom to the ancient Greeks/Babylonians/Etruscans/... would you expect to be most useful? How and why? What does it mean to be useful, anyway? Useful to whom? To them? To us?

Did they come up with that bit of wisdom by themselves and rejected or ignored it, anyway? Would it have been different if it was unearthed as a relic of a past civilization?