> So go ahead, write your own date library, your own Unicode font rendering, compiler, OS, game engine or what ever else people tell you to never do because its hard.

You can absolutely do these things. What you need to be aware of is that in most cases maintaining these things to a production quality level is full-time job for a talented engineer. So you shouldn't attempt these IF:

- You have a higher-level aim you are also trying to achieve

- You need a production quality implementation

If one of those isn't the case then knock yourself out.