Saturday and Friday

While "had lost" is not exactly wrong, it seems overkill when describing recent events in a conversational context, and "lost" would usually be used instead. In a written narrative about historical events, "had lost" seems more desirable.

If today is Sunday then often one would say "yesterday" rather than "Saturday".

Spelling: "because"

Let us take another example.

You visited both Turkey and Greece.

First you visited Turkey afterwards went to Greece.

3.I visited Turkey before visiting Greece.

4.I had visited Turkey before visitng Greece.

Are both fine in this context?

Anonymous3.I visited Turkey before visiting Greece.

4.I had visited Turkey before visitng Greece.

Are both fine in this context?

Yes (except for the typo in "visiting" and the missing spaces after "3." and "4."). However, the second feels more like you are writing about historical events (rather than, say, a recent trip).

I agree, or you use the past perfect because something that you learned/saw/did on the Turkey portion of your trip influenced something you learned/saw/did on the Greece portion of your trip.

I had worked in a factory before I worked at the shipping facility, so I had an understanding of manufacturing-related delays.

So what you are essentially telling me is that the past perfect is not necessary unless it borders some kind of a historical event, in this context.
Obviously your holiday trips don't borders history.
So I have to careful when writing past perfect.
However, I have learnt to write past perfect when pushing one action before the other. This is

I agree:
You don't need the past perfect if it's completely clear what order thing happened in, as it would be with words like "before" or "after."

You do need it when it would not be clear which happened first, as it would be if you linked them just with "when." (We left when she arrived... she arrived and then we left? We were already gone when she arrived? You need past perfect fo

We were taught that because Friday is a specific time so we should use simple past instead of past perfect. Past perfect is to talk about an action happened before another action in the past, and there is no need to state a specific time in the sentence...So, I confuse a litter bit. I think it should be "I lost my wallet on Friday."

microlabSo, I confuse a litter bit. I think it should be "I lost my wallet on Friday."

I'm not sure anyone here is disagreeing with that, assuming you're describing recent events in ordinary conversation.

I have learnt from Grammar Geek it is unnecessary to write the past perfect unless the two past events are not clear to your audience.

Yesterday I went to the bank first. Afterwards I went to a grocery shop.

Yesterday I visited the bank before visiting the grocery shop.

As the conjunction before makes the two events clear, it would be unnecessary to write the past perf

And I agree with you.

However, you may want to emphasize the order of things for some reason.

Because I had visited the bank before the grocery store, I was able to pay cash for my groceries.

The PP isn't necessary there -- you have "before" to make it clear, but maybe you want to emphasize that you did things in that order (bank first, grocery store second) to show yo