YOU SAID:
Because you never know when a rock is going to fall on your head
INTO JAPANESE
いつ岩が頭に落ちるかわからないから
BACK INTO ENGLISH
I don't know when the rock falls on my head
INTO JAPANESE
いつ岩が頭に落ちるかわかりません
BACK INTO ENGLISH
I don't know when the rock falls on my head
That didn't even make that much sense in English.