YOU SAID:
I do not know how people are so stupid
INTO JAPANESE
どうして人間はこんなに愚かなのか分からない
BACK INTO ENGLISH
I don't understand why humans are so stupid
INTO JAPANESE
なぜ人間はこんなに愚かなのか理解できません
BACK INTO ENGLISH
I don't understand why humans are so stupid
You've done this before, haven't you.