I'd like to know the reason why you're so late.

我想知道你为什么迟到那么长时间。

《牛津词典》

I'd like to know the reason why you didn't accept his advice.

我想知道你不接受他的建议的原因。

youdao

I always think of you, but I always fail to know the reason why.

我总是在念着你，但是我不知道我想你的缘由。

youdao

And this is the reason why enthalpy was invented and why it's so important. Because we want to know this. So this for a finite change.

这也就是为什么焓要被提出,而且如此重要的原因,因为我们想要知道这些。

麻省理工公开课 - 热力学与动力学课程节选

Solution focused wants to know the reason why.

FORBES: Four Signs a Relationship Is Failing

Would you like to know at least one major reason why the stock market keeps going up and up?

FORBES: Fed Juice Has Always Helped Stocks Sprint Higher

And that's part of the reason why I decided not to go for, you know, too much of a hard image, you know, never to pick up a gun in the piece, you know.

NPR: 'In The Mix' Marks Usher's Film Debut