If you're already in orbit around something (Earth, Sun, etc.) then it's pretty expensive and hard to crash into the thing you're orbiting, but if you're trying

If you're already in orbit around something (Earth, Sun, etc.) then it's pretty expensive and hard to crash into the thing you're orbiting, but if you're trying to go from one body to another there's lots of ways you could drive straight into the thing by accident. A minor miscalculation on a slingshot approach sends you straight into the planet instead. That we hit Mars with the lander by accident should demonstrate it's not only possible, it's actually not that hard.