If you want to land on an asteroid/rock, either you match speed with it, in which case you already had enough speed to go wherever it's going, or you intercept it at a different speed, in which case you get smashed to dust if your speed was any more than a few m/s different.

Maybe you didn't mean this, but it's a common enough misconception. People even on HN were suggesting a spacecraft could hitch a ride on ʻOumuamua to get a quick way to a different solar system.