Comment by nly

Depends what "doing it badly" means.

The most important aspect of software design, at least with respect to software that you intend not to completely throw away and will be used by at least one other person, is that it is easy to change, and remains easy to change.

Whether it works properly or not, whether it's ugly and hacky or not, or whether it's slow... none of that matters. If it's easy to change you can fix it later.

Put a well thought out but minimal API around your code. Make it a magic black box. Maintain that API forever. Test only the APIs you ship.