Yeah, I inherited this giant gob of shit at work that someone had made a year or two ago to generate quotes for the company's buyers. It had everything - giant databases over multiple sheets, formulas of all varieties, hundreds of named ranges, hand-made macros, back-end sheets... and no comments or documentation anywhere. Plus, the person who made it didn't even work there anymore. Since no one else there was particularly good at Excel, I took on the task of updating it and making the additions they needed. It was definitely the best self-teaching experience I've ever had.