From time to time it falls upon my lot to read parallel accounts of the same event , and I find this to be deeply interesting from the point of view of someone looking for insight on sources and how it can be obtained. The sort of parallel accounts I read generally fall into two types. One of these types is made up of parallel accounts from different but not necessarily hostile perspectives. Examples of this can be the comparison between 1 and 2 Samuel and Kings and the distinct parallel account in 1 and 2 Chronicles as well as the four Gospels in the Bible. A non biblical example of this includes many of the stories in Century Magazine where Civil War generals and other officers presented their own perspective so as to show how a given battle looked to them, usually with some sort of aim at clearing their own name and reputation from the harm of alternative facts. This last type shades a bit closer to the second type of parallel accounts, and that is where one sees two very distinct sides of the same story that are in conflict with each other, like the one-sided narratives of divorced parents that I have heard since childhood. This is, therefore, a sort of matter that is of interest to me as both a patient listener to the stories of other people and a student of historiography, especially given the rampant increase in obvious bias over the last few decades within many fields as any attempts at fairness and evenhandness in approach have largely been given up for partisanship.
Why do we need parallel accounts in the first place? Isn’t one account enough? Some writers, going back as far as Tatian at least, took complicated accounts like the Gospels and telescoped them into one view in order to get rid of apparent textual difficulties that resulted from comparing the accounts together. On the one hand, this might seem like a sensible thing to do, but we are often not well equipped to fully understand what happened in the past, and often the multiplicity of accounts lets us know just how complicated something appeared. Also, there are subtle hints that one can gain if one looks between the lines. For example, in the syntoptic Gospels there is a healing account where Matthew preserves that there were two people healed while the Gospels of Mark and Luke record one person being healed, without there being a contradiction in this. From Matthew we learn that there were two people and thus the situation met the biblical standard of factuality which required two independent witnesses to corroborate something, while the other Gospels focus on the more visible and talkative of the lot. Without all of the perspectives we would lose something about the scene, and details would be lost in either harmonization unless it managed to capture the full meaning provided when all accounts are viewed together. Examples like this could be multiplied.
This is especially an important matter to consider when we are dealing with hostile accounts. At times the accounts of two sides in opposition may seem impossible to put together in any kind of coherent narrative. When I was a child, for example, being shuttled on breaks between my estranged parents, I would regularly hear each of them telling their own side of the story. Being the sort of person who saw elements of both of my parents within me, a thought that still terrifies me from time to time, I fairly quickly developed a hermeneutical approach to deal with the varying details, by which I figured that both parents would be honest in telling the flaws and offenses of the other but would omit their own flaws. That is, I saw readily that both of my parents would suppress any matters that would reflect badly on them but would seek to be as candid about that which made the other look bad. And, putting the two variant accounts together, I saw two people who had made a somewhat dishonest bargain and spent so much time justifying themselves and their own behavior that they forgot to take care of their own moral conduct, their own behavior, or to care for their children. It is a pattern I have seen happen over and over again in relationships as well as in dysfunctional political cultures, where a focus on self-justification short-circuits the crying need for reflection, repentance, and reconciliation between estranged parties.
There are plenty of reasons why we need parallel accounts. For one, no one can understand and no one is likely to admit the whole truth. Once we have an understanding of the perspective where someone is coming from, we can adjust their accounts accordingly while still recognizing their value even as partial sources. Likewise, sometimes even where accounts are not deliberately or completely hostile the very apparent discrepancies that we see can let us know just how chaotic and complicated a situation was, which allows us to be more understanding to the decisions that were made by all parties involved. Given our own difficulties in recognizing and remembering and coping with the stresses and drama of life, knowing that the lives of others were the same sorts of lives is something that gives us some much-needed empathy. And ultimately it is that ability to see the same things from many different angles, and the understanding of ourselves and others, the present and the past, that results from this ability to shift perspectives that makes parallel accounts worthwhile. Sometimes one has to read the same story two or three or four different ways to really understand it at all.
 See, for example: