Anders Pedersen shares an easily-avoidable tale of woe:
ETL. Spec said only Address Line 1 is needed to be loaded, so the developers only bring that line in (plus name, city etc.). Fast forward 8 years, I get a request on my desk: “Please add Address Line 2 to import, and all tables. Oh, and we need historical data for previously loaded files. And for all address types”.
Groan.
No normalization in this database (which is just one of about 40 databases with SIMILAR structure, but not identical).
Read on for the damage done, as well as another example of foresight saving the day.