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...