In Spanish, When is it right to use Es rather than Est�?

In the first example, estar should be used, because it is a temporary occurence and will not be present very long. In the second one, ser should be used, because stupid is a basic trait of character. These are the rules when each of them should be used. Estar is used for locations and temporary conditions, ser is used to tell the time (son las ocho = it's eight o'clock) and for basic traits of character.