ばよかった
Usage
Used to express regret about past
Examples
漢字が書けない。学生の時、もっと勉強すればよかった
I can't write Kanji. I should have studied harder when I was a student
頭がいたい。昨日あんなにお酒を飲まなければよかった
I have a headache. I shouldn't have drunk so much yesterday