If the speaker is telling a story from a past tense perspective, everything that happened before that time is in the past perfect: "When I visited China in 1985, I couldn't believe that so many people could live in one place. I'd grown up in a small southern town with a population of 1000." Here, for example, the author sets the time of his discourse in the past by starting his story with "When I visited China in 1985." Then he refers to his own childhood, which was obviously before his visit to China, using the past perfect "I'd grown up in..." Now let's look at how he would tell the same story from a present perspective: "I just came back from China. I can't believe that so many people can live in one place. I GREW UP in a small southern town..." because from a present perspective, everything that happened before NOW is in the simple past. I hope this makes sense - if not, please ask. Happy New Year!