Actually, there is a slight difference between "Tú fuiste..." and "Tú eras...", even though both are translated into "You were...".
- "Tú fuiste un médico..." sounds like an action in the past. It's used in biography when we cite all of the actions that someone did, and all of the jobs he had. It's a bit like the English "You have been ...", except it has no relations with the present.
- "Tú eras un médico..." is a description in the past. In a story, all the actions would be performed while he was a doctor.
You are right, I'm native spanish speaker and sometimes is a little confuse when you want to use era(s) with "fui(ste)".
You can used "fuiste" when the sentence express emotions (frequently positive) for example if you want to give good news to anyone:
¡Carol, fuiste aceptada! // Carol, you were accepted! (I think correct translation: you've been accepted!)
Because "¡Carol, era aceptada!" doesn't sound native.
I would like a native Spanish speaker to back me up that the literal implication of using "fuiste" is that the person in question is no longer a doctor. However, perhaps the "doctor" is now retired, and for this reason, which is that this retirement is a permanent state, AmineHadji1 is right because the English words "you have been" can be used to speak not only of actions but also of states that occurred the past, with the present state being that you are no longer a "famous" doctor.
What is problematic here is that, in both English and Spanish, the conjugation "have been" is in the (present) perfect tense. However, the connotative meanings are different in each language because the Present Perfect Tense conjugation of the English infinitive "to be," which is "have been," can be translated as either "ha sido" or "ha estado."
If I understand the Spanish connotative meanings correctly, "estado" is used for an action that was ongoing in the past but may or may not have stopped. For this reason, I would translate "ha estado" as either the literal "has been" (the action stopped) or as the connotative "was being" (the action started in the past and is still continuing)."Sido," if I understand the nuance correctly, is used for states that occurred in the past and also ended in the past. That is, "you" are no longer a "famous" doctor. For this reason, I would translate "ha sido" as either the literal "has been" or as the connotative "used to be."
Although "ser " and "ir " look the same in the preterite, sentences with each are constructed slightly differently. To say "went to" you need the preposition "to," which is not present in the drill sentence.
"you went to a very important doctor" = "fuiste a un doctor muy interesante"