動詞仮定形よかった／動詞（ない形）なければよかった

Meaning

This pattern expresses regret about something you did or didn't do in the past. 動詞仮定形よかった expresses regret that you didn't do something, wishing you had done it instead. 動詞(ない形)なければよかった expresses regret that you did do something, wishing you hadn't done it. Both can take のに at the end for emphasis. The more casual spoken form of the negative version is なきゃよかった.

Formation

Examples

1. 友達は私の話に傷ついたみたい。あんなことを言わなきゃよかった。
   My friend seems hurt by what I said. I wish I hadn't said such a thing.

2. 昨日の学園祭に来ればよかったのに。とても楽しかったよ。
   I wish you had come to the school festival yesterday. It was really fun.

3. あんなに恐ろしい映画、見なければよかったなあ。
   I wish I hadn't watched such a scary movie.

Summary

• 動詞仮定形よかった expresses regret about not doing something you should have done
• 動詞(ない形)なければよかった expresses regret about doing something you shouldn't have done
• Both patterns convey past regret; can add のに for stronger emphasis, or use なきゃよかった for casual speech