I mean, dining philosophers is very simple as well. Dijkstra’s shortest path is simple.

Simple can still be difficult to understand.

It sounds like your definition of “simple” is more like “short” than “straightforward”?

Simple as in the opposite of complex.

Simple doesn’t have to be easy.

If your definition of 'simple' varies that drastically from mine, it might follow that your definition of 'complex' varies likewise. I guess we just use these words in different ways.