Another fun thing I didn't really understand all that clearly until I spent time playing KSP: Why it's theoretically easier to get to the Sun from Pluto than it is to do so from here.

Related: my mind was blown when I realize how easy it is to fall down to Earth (well, Kerbin) if you're in high enough orbit. I've had cases where my orbital velocity was on the order of 200 m/s, which means that at apoapsis you can just fart, and have the satellite crash into the ground a day later.

(I've also had my fair share of high-orbit missions where in the middle of the launch I realized I'm aiming for a prograde orbit, where the contract specified retrograde. Instead of reloading game from launchpad, I just carried on, put my apoapsis at target altitude, and once reaching it, burned off couple hundred m/s of Δv to reverse the orbit's direction.)

The point isn't really for it to fall into the sun, just to push it to some kind of orbit that is irrelevant to the space junk problem.

Orbits are periodical. Anything you throw at the sun will come back up to the same height soon enough.

(Ignoring smaller effects)