The main cause of people not racing to their potential is starting too fast. Even runners who have sworn to run even pace from the gun lose their heads in that first mad dash off the line. They get sucked into starting too fast, in part because the people they want to beat seem so far ahead.
Ignore the madding crowd in the first third of races. You’re not obligated to run lemming-like and follow others who are botching their performances by starting too fast. If you want to beat specific people, the way to do that is to be ahead of them at the finish line, not the 1-mile mark. Running the fastest time you’re capable of on that day will almost always mean running the same pace throughout the race. Do that, and you’ll catch the too-fast starters by the last third of the race. As you pass them, they’ll be unable to respond because they’ll be too busy paying for their early-race brashness.