After figuring out how to do most things successfully in Kerbal space program, a fun challenge is to install the "real solar system" mod which scales the delta v require for low orbit, and size of the solar system , up to approximately the same as reality. Delta v to orbit in stock KSP is like 2300-2500 if I remember right, in RSS it's 7800-8200. Everything else is also correspondingly more difficult like delta v require to get from a 35 degree inclined low earth orbit into a mars transfer orbit (even assuming 100% aero braking at mars and little or no fuel used at arrival)