Refactoring is great, but there’s more.

The larger a project is or the busier developers are, the harder it is to become acclimated to parts of the code, too.

There are a few more examples from the article:

Bugs pile up. The build slows. Backwards compatibility imposes its own tax on progress. Original team members move on, while new members take time to acclimate.

He doesn’t mention this, but it also takes time to re-acclimate yourself to things you wrote six months ago. Good code and tests help but developers are human beings.