When exposed to the German education system, you'll pick up the importance of methodology and planning. In the Business Administration classes, we learned how important it is to do your strategic planning (10+ years) and operational (2+ years). OK, in the late 70s the world turned a bit slower. So when introduced to the presessors of RUP (Rational Unified Process), a heavy top-down, big-bang approach seemed very sensible. Well, it worked (somehow) and I thought I just have to improve my planning skills and spend days with Rational Rose trying to get the full round-trip to work.
When starting Compiere in 1999, I know I had to do something else. Especially with Open Source, the traditional Big Bang approaches did not seem to work. So, I thought, I have to start "without a methodology". After a while, we managed to publish stable daily releases and incorporated feedback very quickly. Initially users and customers were concerned about using the daily releases in production, but our track record was persuasive. So, it became standard procedure to use a daily build in production, especially if an important bug fix /improvement was made available.
One day, a friend told me that "our agile approach" was working nicely. I was surprised that what we did had a name - so looked it up and was astonished to find the pricipals I was living actually written down. Happy to have found a name for what I was practicing for quite a while, I signed the Agile Manifesto in early 2002