"I called him" just states the fact. "I did call him" emphasises the fact, especially if spoken and the speaker emphasises "did". "How did you contact Jim?" "I called him." (I didn't send a letter, or an email, or knocked on his door). "You forgot to call Jim". "I did call him." (I didn't forget it, and if he claims I did, he is lying).
To answer a question "Did you call Jim?" you would answer "Yes, I did." or "No, I didn't".
The choice of tense here is somewhat restricted by the meaning of expect, which means to anticipate that something will happen. When we expect something, we believe it will happen; we await it.
When that which we expect to happen turns out to happen or to not happen, we no longer have the expectation. The expectation is abandoned either because now we know otherwise, or because what we expected to happen has indeed happened. When it has rained cats and dogs and our shoes are already ruined, we cannot expect them to get ruined. We cannot expect the 4PM train to be late if it is 4PM and the train has already arrived on time.
If we are speaking of an expectation as either an ongoing state of mind or as an abandoned state of mind, we do not use the present perfect with expect . If the expectation is abandoned, it is a thing of the past.
What did you expect?
What were you expecting?
If the expectation is ongoing, it is a thing of the present.
What do you expect?
What are you expecting?
Only when we wish to speak of the expectation as one that may be in transition from held belief to abandoned belief does expect hook up with the present perfect, though even then the two are awkward dancing partners.
What have you been expecting?
What have you expected?
What have you been believing?
What have you believed?
The present perfect could also be used to mean "things that I have believed over the course of my lifetime which I no longer believe, but I own to having believed them".
Have you expected Santa Claus to come down the chimney?
Have you expected the Tooth Fairy to leave money under your pillow?
Have you expected business partners to be honest and above-board?
Best Answer
The exact difference is 100% in how the speaker is choosing to frame the event in time. There is no objective difference between them.
In the first, the speaker is choosing to treat the state of sitting as a single event; in the second, as an event extended in time.
The reasons for the speaker's choice cannot be answered without more context. Some examples of reasons they might have are: