Questions about Ser and Estar
Q: Why is it soy estadounidense and NOT estoy estadounidense?
R: Use ser for nationalities, which are a part of a person's identity.
Q: Why is it estoy cansado and NOT soy cansado to say "I'm tired?"
R: Cansado is used with estar to mean "to be tired." Only use ser if you want to say "I'm tiring" (i.e. a tiring person to others).
Q: Why is it el concierto es en el estadio and NOT el concierto está en el estadio?
R: Remember that you should use ser to describe the location of an event and estar to describe the location of other things.
Q: Why is it la gata está muerta and NOT la gata es muerta?
R: You should always use estar with the adjective muerto. You could perhaps reason along the lines that being dead is a condition or change of state, not an identifying characteristic.
Q: Why is it soy de Canadá and NOT estoy de Canadá?
R: Although estar is often used for location, you need to use ser to indicate place of origin.