I got bored of shooting one car by itself, and when Chris and Ralph came by close together, I set up to get a shot of them the next lap they came around, figuring I'd have the two of them close together. Camera (D3) was on burst mode, so I'd get "my" shot, followed by several more as the camera shoots about ten images a second. Well, they came to the turn, I pressed the button, and got the whole sequence, this just being one of the shots. It's not what I was after, not what I was expecting, but I just held the button down until the action was over.
I did this many times - this and a photo of Maxy and Joaquin were the ones where it worked best. It helps to plan ahead, but then sometimes you get lucky too!