One of the most important aspects of movement is the ability to deceive defenders and get them to "lose track" of one's path. Any time there's a defender "marking" a player, that defender has to attend to the player's path in order to "stay with" the player, but also has to track the path of the ball in order to know how to position himself and generally know what's going on in the game. This requires a constant shifting of visual attention between the ball and the relevant player. The most effective runs, therefore, are often initiated while the ball is moving. That is, a defender is much more likely to lose track of an attacker, and not follow his run, when the run is started while the ball is being passed from one player to another, because it's harder to track two moving objects than one moving one simultaneously with another stationary one.
In addition, there's one type of run that is particularly difficult for defenders to track while they track the ball: runs that cross the path of the ball. I'm quite surprised that I've never heard anybody make note of this fact, whether commentators, coaches, or writers. [For two random examples that just popped into my head see Germany's second goal against England (~1:10 in the video) from Monday, and Holland's first goal against argentina in 1998 (~50 seconds into the video). Notice how awesome these goals are because of the cross-ball-path runs by Muller and Kluivert respectively...they completely catch their defenders "ball-watching"] The reason these runs work so well is the same reason that crossing voices are hard to follow in counterpoint...apologies for the convoluted music analogy, but it works really well here. What happens is it becomes much harder to identify the two paths accurately as separate "streams" or separate "objects" in the mind because as the player's head turns to track the ball the path of the player goes in the other direction. As long as the paths remain distinct and separate, the defender's task is much easier; when a player's run crosses the path of the ball, the two paths become confused, and the defender inevitably attends to the ball over the player.
Germany are the best team so far in the World Cup at making these types of runs. Spain and Argentina are more technical, and also good at confusing defenders with their movement, but Germany are really shockingly good at it.
Of course there are other relevant things to talk about here, especially coordinated movements between different attacking players to intentionally distort an opposition team's shape or positioning. That'll be for another time.