It’s tricky. Trying to analyze it now I think “estar” should be used when describing a current / short term state of being. And “soy” should be used to describe a permanent or long term state of being that’s not easily to change. I’m happy. (A current or short term state) Estoy contento. I’m American. (A permanent / long term state) Soy americano. I’m drunk. I’m sober. (A current or short term state) Estoy ebrio. Estoy sobrio. But even if someone is always sober, I don’t thing in Spanish we say “soy sobrio”. It’s hard to explain why. Maybe it’s because the state of being sober can easily be changed. Other ideas?

Es is used to access neicateba permanent state, whereas esta is used to indicate a temporary state.