[animal531]

I think I know what you mean, but I'll counter and say that instead of just focusing on completing the game one should pay some attention to longevity and re-usability of your codebase.

For example I have things like a KD-Tree implementation/wrapper that will always be useful, a maths library, a HexGrid component I use a lot, wrappers for rendering a lot of things fast, an entity system for units/objects, a generic framework/layout for code/objects in Unity etc.

But having said that, it really depends on the type of game that you're making.