We would use this expression to describe a crushing disappointment or a truth hard to bear. Let me see if I can offer some examples. A man thinks his job is secure. He is doing well in his work. One day, without warning, his boss tells him that due to a reorganisation of the company, he is being terminated. It was a bitter blow. Or, a woman has been happily married, so she thinks, for years. One day, without warning, her husband announces that he does not love her and has decided to leave her for another woman. It was a bitter blow. Could one say? C'était un coup amer or would it be un coup dur ? What comes naturally to mind? Merci d'avance.