As I know, both Simple Past and Present Perfect can be used for an action that happened in the past. However, S.Past is used for an action which has a definite period of time whereas P.Perfect is used for an action which doesn't have a definite period of time. Am I right?
I'm confused about these two tenses. Can anyone explain the differences between them? Let's take an example (Your friend - B, You - A)
A: What did you do last night? Was there any fun?
B: No, there wasn't any fun. I already broke up with my girlfriend.
A: What? Why did you do that?
Case (2): (You and your friend haven't met each other for a long time)
A: Hey, what have you been doing?
B: Everything is so boring. I have broken up with my girlfriend.
A: What? Why have you done that?
In Case 1, I use "Why did you do that" - (Simple Past) because I know that he broke up with his girlfriend last night.
However, In case 2, I use "Why have you done that" - (Present Perfect) because I don't know when he broke up with his girlfriend (Maybe yesterday or 1 week before, 2 months before,...)
What do you think? In my opinion, in most real conversation, we can use "Why did you do?" and "Why have you done?" interchangeably? Am I correct?