Imagine you're truly immortal, in space.

You jack it. Eventually, you will ejaculate. That ejaculation will give you a tiny, miniscule amount of thrust.

You jack it again the next day. Hell, maybe that same day, I don't judge. Same result. You shudder, a tiny amount of thrust.

Then again. And again. And again, over eons.

You will go faster and faster. Incredibly slowly, yes. But faster still. This is how ion engines work. Tiny amounts of thrust, but over long enough time scales you get serious results.

Eventually your jacking will propel you to an appreciable fraction of the speed of light. You'll be propelled across the cosmos at the end of light years long stream of gossamer wads.