Festering code bases and budding code bases

A truly excellent read:
http://michaelfeathers.typepad.com/michael_feathers_blog/2010/06/festering-code-bases-and-budding-code-bases.html

Especially the concept that at the time of change, just adding code to an existing method, and not refactoring to a better structure, is perceived as more cost effective, but it’s just accumulate technical debts, that over time cost money in the form of interests. Same concept can be applied to write unit tested code: it seems to cost more at the time of change, but costs less in the long term, by flattening the curve of cost-of-change.