Momentum; not so much the ability to keep going as the inability to stop.

The beauty of it is that he'll come to you. He's been set in motion, and in that moment, he forfeited the decision to stop. Robin's been building up momentum for years, and now he's on a collision course.

You intend to be waiting at the end of it, pinning him down despite the speed and keeping him down.

He's yours now. It's only a matter of time.