There is a persistent myth in the running community that there is no "best" or "correct" technique for running. It is common to hear statements indicating that everyone will naturally adopt a technique that is best for them, or that runners will naturally improve their technique just by running more. In fact, many people in the running community become indignant at the very suggestion that maybe what constitutes good technique is not a matter of choice. Unfortunately the laws of physics do not change according ones beliefs.
For every other sport or athletic activity, of which I am aware, there is very little argument over the need to learn correct technique. There is no assumption that most people will naturally adopt the best technique for that particular activity, and learning correct technique is usually the first thing on the agenda upon starting a new sport. However, for some reason, most people seem to believe that running is an exception.
The vast majority of people in the world have bodies that are nearly identical in constructions and proportion. Yes, of course there are variations from person to person, but very few people are so significantly different from the norm that those differences would require them to move in a dramatically different way. The human body can simplistically be thought of as a mechanical system, and every mechanical system, will have an optimal way to move based on the laws of physics. The greater the variation from what is optimal, the less efficient the movement will be. In principle this is something that can be calculated, and is therefore something that, in principal, can be proven.
Currently there are dramatic variations in the way people run, despite the fact that they are built the same way, albeit with some small variation. The small variations from one person to another may require some slight alteration in technique to reach optimal efficiency, but not enough to explain the dramatic difference in running technique seen among runners today. The idea that that everyone should do whatever "works" for them is very popular, but it has resulted in a very high rate of injury.
Let me point out that running is natural, but we do not live naturally. Most children, without any special training, start running with good technique. For most of human history, once a child learned to run, he or she would have had to run regularly though out his or her life, and it would have been done barefoot or in minimalistic shoes. The result would have been that once the skill of running was learned, it never would have been lost. Today children learn to run just as they always have. However, they are quickly put into shoes, and usually end up adopting a very sedentary life style by the time they enter school. So for most people who decide to take up running later in life, running is a skill that they no longer possess.