A beat is like a down. A new foothold has been established. There was a play (a plan), a skirmish (conflict) and an advance was made toward the endzone (goal).
There are first downs and also downs of lesser importance, which establish a rhythm of forward motion, including an occasional setback. Sometimes you get a new first down all in one big exciting swoop, sometimes you grind it out, sometimes you’re at third and eighteen and you’re down by seven with a minute to go. The next beat is going to be the big one.
You don’t repeat a beat. Once you make that down, you don’t have to ever play it again. Never write a scene without some kind of new beat in it. Whether it’s in action, character development, a relationship. The same beat is ground you already covered and the clock is running.