分わかったもんじゃない

expression

there's no knowing; it's anyone's guess; who knows?

Colloquial expression used when a situation is unpredictable or when someone's behavior is hard to read. Often implies that the outcome is uncertain or that people can be surprising.

• あの人ひとの考かんがえてることは、分わかったもんじゃない。

  There's no telling what that person is thinking.

• 明日あしたの天てん気きなんて、分わかったもんじゃないよ。

  Who knows what the weather will be like tomorrow?