Past perfect vs past simple confusion

Jack often has solid and correct answers. So I apologize that I will try to add. I am more simple than Jack, so I state things more simply, but I hope this is helpful.

The past perfect is for story telling. When you are telling a story of a past even, the past perfect it what you use to tell a story of the past INSIDE a story of the past. A dream within a dream. “Four years ago I thought about my past, I had been working for 2 years...”.

Past simple is more flexible but les precise. “I was working for two years.” Doesn’t say when. I could be from today. I could say “this happened back when I was working in japan for two years”. This could mean the event happened at any point in my two year stint working in japan.

With simple past, you are talking about the past from a perspective in the present:

My hair was uneven for years, but now I have cut it all off.

With past perfect, you are talking about a remote past, as seen from a more recent past:

Two years ago, when my hair had been uneven for years, I cut it all off.