From The Handbook of Research Analysis and Meta Analysis:
Searching for information for a literature review is a big like a treasure hunt. But there isn't just one treasure chest! It's like many pieces of treasure were dumped overboard and now you have to retrieve as many valuable pieces as possible. "Unfortunately, there are reefs hiding pieces, currents have pushed pieces about, and since it was strewn about many years ago, much of the treasure is covered by sand and plants. It will take a lot of effort to retrieve each piece of treasure. But because the pieces of treasure complete a puzzle, it is important to find every piece of the puzzle that you possible can to unlock the secrets of the puzzle."