More than half for me, back in 1994 I wrote a 360° 2D platform scroller in assembler and figuring out how to do tiling, scrolling, clipping, rain effects, paral

More than half for me, back in 1994 I wrote a 360° 2D platform scroller in assembler and figuring out how to do tiling, scrolling, clipping, rain effects, parallax, collision detection, audio and video on my own from scratch in a single thread of execution was more fulfilling than designing and creating levels and is the reason I never finished it. The only algorithm I looked up was bresenhams for drawing lines. Of course I can see why many people would want to avoid that and focus on other aspects. These days I have less time so I leverage libraries and try to finish projects ;)