On 6 May 1954, Roger Bannister ran a mile in 3 minutes 59.4 seconds at Oxford. The four-minute mile had been treated as a wall. Within weeks, someone else ran faster, and then the barrier became a result people expected. The interesting part is not the watch. It is how quickly a limit, once broken in public, stops looking like a law.
Once a public limit is broken, other people cross it as if it had been ordinary.
The marathon's odd distance, 42.195 kilometers, comes from the 1908 London Olympics. The race was set at 26 miles and then extended 385 yards so it could finish in front of the royal box. That particular length was later adopted as the standard. A world record is measured against a walk that was lengthened for a viewing stand.
The marathon distance is the 1908 London course, kept because it became the rule.