Nobody knows, but there's a theory which won't answer your question but will put it into a broader context.

没有人知道答案,但有这么个理论,它无法回答你的问题,但却能让你从更宽广的视角来看这个问题

耶鲁公开课 - 心理学导论课程节选

There is obviously no magic solution to this question but the best answer I know of is Socrates.

这个问题,没有神奇的解答,但我认为最佳的答案是苏格拉底。

耶鲁公开课 - 政治哲学导论课程节选

Very good yes, and that's a big argument that nobody has a good answer for.

好问题,还没有人给出令人信服的答案

耶鲁公开课 - 古希腊历史简介课程节选