Past simple vs present perfect [duplicate]

I have read many online articles. I've read questions and answers on this site. I still can't get my head wrapped around the difference between past simple and present perfect

I know the difference is between finished time (use past simple) and unfinished time (use present perfect). But as a non-native English speaker, this still makes no sense to me. I am not implying any kind of time period.

I have posted on SE
I posted on SE

I just want to convey that the action completed in the past. I don't want to provide any connotation whether the action just completed, or completed at certain period in past.

Maybe with "I", I know the time period, but what if I am talking about someone else.

He has posted on SE
He posted on SE

I don't know the time frame that "he" did the action. I don't know what "he" was planning (continuous action, or at specific time). I just know the action took place in the past. I don't know if it just finished. I don't know if there is a consequence to the action or not.

It seems to me that I am forced to imply a time frame. So my question is: if I don't want to imply any time frame, or at least to imply as little as possible, what should I use?

Solution 1:

It's not a time frame you are forced to convey, it's a way that you are viewing the relationship between the event and now. In many cases, both forms are equally valid in referring to one and the same event, but differ in how you are focussing your attention.

So unless there is some external context that limits the time, I have posted on SE and I posted on SE mutually imply each other. But in the first case the speaker is choosing to view the event as within a period which includes the present. As Peter Shor says, the simple past is more neutral.