In most cases, these rules started out as a lightbulb over one runner’s head. After a while, that runner told a few running buddies (probably during a long run), word spread, and before you know it, coaches were testing it, sports scientists were studying it, and it evolved from idea to theory to accepted wisdom.
Along with each of the rules we present, however, we list the exception. Why? Because, as you also learned in grade school, there’s an exception to every rule.