Nothing fancy. I was in the BI department of a big telco and I inherited a "next best offer" system. It was extracting data from the DWH, doing some scorecard based optimization, picking the right product for the right customer and sending the results to the call centers. The data extraction part was a PL/SQL framework and the optimization was done by a SAS tool. The system was really slow: after a change in the parameters it took 48 hours to recalculate the results. Unfortunately the product line managers loved to change the parameters on the day of the data delivery and my team lead couldn't say "no". So after a couple of month I ended up doing almost everything manually in order to keep the product line managers happy and to keep the deadlines. Practically I took the system step by step to pieces and I worked with standalone SQL scripts, like back in the 90's. After a lot of people were fired and my team lead resigned I was left alone for two months. There was practically nobody to require urgent changes so I used my time to rewrite almost everything from scratch, included the features the product line managers wanted and reduced my monthly workload from 25 days to 3. And I didn't tell about it.