It's a mystery to me.

这对我来说是个谜。

《新英汉大辞典》

It's a mystery to me how it all happened.

这一切是怎么发生的，对我来讲是个迷。

youdao

It's a mystery to me how she passed the exam.

她是如何通过考试的对我来说是一个谜。

youdao

' But it's a mystery to me, man.

CNN: Does Brad Pitt suffer from face blindness?

It's just a mystery to me that it's taken a civilised society so long to bring in a law which protects those of us who care about our health, as opposed to those who indulge in the disease-sticks.

BBC: Non-smoker

"It's no longer a mystery to me why Microsoft's offer isn't around, " Icahn told The Wall Street Journal.

FORBES: Jerry's Gotta Go, Icahn Says