The lunar module was neither self-landing nor reusable.

The lunar module was navigated and landed by a human pilot (with computer assistance).

The descent stage stayed on the Moon, and wasn't reused (except as a launch platform for the ascent stage). The ascent stage also wasn't reused - after the astronauts exited from the ascent stage into the command module, the ascent stage was jettisoned to crash into the lunar surface (or sent into solar orbit). Only the command module returned to Earth.

https://en.wikipedia.org/wiki/Apollo_Lunar_Module

There is an implicit "on earth". Gravity wells being vastly different. If the earth was bigger then we wouldn't even be able to get to orbit.

Wouldn't we just need to generate more velocity?

Easier said than done. Rockets have to carry their own fuel, so they are heaviest at launch. If you’re in a deeper gravity well, then you need a longer burn to reach escape velocity, and then also more thrust at launch because you have to carry more fuel (which means still more fuel...)

It never becomes mathematically impossible to achieve escape, but it can become engineering-impossible, ie the propellant fraction becomes so high that it’s impossible to build a structure that can contain the propellant and maintain mechanical stability. Just for reference, modern rockets are 90+ percent propellant by mass.

For more, see https://www.nasa.gov/mission_pages/station/expeditions/exped...