[omgbear]

It's harder to learn the impact of your design decisions -- Seeing how software evolves to meet changing business goals and how the design choices made play out in the long run helped teach me a lot.

Coming up with a neat API that turns out to be difficult to modify in the future, or limiting in ways you didn't imagine would when writing it is a good learning experience.

Or seeing how long a system can survive growing usage -- Maybe a simple hack works better than anyone expected because you can just pay more for RAM/CPU each year rather than rebuild into a distributed fashion. Or the opposite, maybe there's some scaling factor or threshold you didn't know existed and system performance craters earlier than predicted.