いい薬くすりになる

expression, godan verb (-ru)

learn a lesson; be good for someone

Typically used when an unpleasant or difficult experience serves as a valuable lesson or beneficial medicine for personal growth. Often implies that the experience, though tough, will ultimately be good for the person.

• 失しっ敗ぱいはいい薬くすりになるから、あまり気きにしないで。

  Failure is a good lesson, so don't worry too much about it.

• 厳きびしい指し導どうが彼かれにはいい薬くすりになった。

  The strict guidance turned out to be good for him.