What's "hard" mean here? Doesn't "hard" mean "difficult?"

Native speaker’s answer
Rebecca
It can mean "difficult," you're right. But here, it means "intensely" or "diligently." To do something with a great deal of effort! Ex: I worked so hard at exercising this year, and I can see the results now. Ex: The kids work hard at school. Ex: You were focusing so hard that you didn't hear me call your name.