We never know why a person ACTS the way they act.

我们永远都不知道为什么一个人会那样去做。

youdao

We will never, ever know why they did that to him.

BBC: Liverpool teenagers sentenced for homeless man's murder

We'll probably never know exactly why this was the case, but at least the Wii is all over the black market, ironically.

ENGADGET: China's complicated history with video games: when a ban isn't really a ban

Why, we will never know.

WSJ: An Accidental Trip to Trans-Dniester | Traveler's Tale