be foolish

That decision is foolish.

その決定は愚かです

That decision about the situation at the time is foolish.

その決定は当時の状況を愚かです

That decision, made without properly checking the situation at the time, is foolish.

その決定は当時の状況をきちんと確認せず愚かです

That decision, made without properly checking the situation at the time and going on rumors alone, is foolish.

その決定は当時の状況をきちんと確認せずうわさだけを愚かです

That decision, made without properly checking the situation at the time and simply believing the rumors alone as true, is foolish.

その決定は当時の状況をきちんと確認せずうわさだけを信じたまま愚かです