While there are areas where my functional convictions have greatly diminished, my mid career zeal had the tremendous benefit of illuminating new architecture and data design principles.

Storing data as discreet changes and relying on pure function selectors to calculate values is wonderful.

It's not always a viable approach at scale (at least not for my ability in certain circumstances) but, when it is, testing is a breeze and I love being able to debug forward/backward in time with consistent results guaranteed.