I had a co-worker who was an experienced software developer but had never worked on a system that interfaced with the physical world before.

For quite a while, he hated having to test on real hardware because all sorts of failure modes that he couldn't predict: belts stretching, mechanisms hitting each other or not lining up properly and losing position, etc. kept happening and interfering with his nice "this will only take 15 minutes to test" estimates, making it an all-afternoon affair.

OTOH, it was that unpredictability and having to deal with weird stuff that I liked about programming embedded systems.