Ask HN: Concepts You Unlearned in Software?

From University, I learned so many beautiful theories, but most of them added unnecessary complexity to my day-to-day engineering. Examples: 1. Using distributed queues - I now just use a database and do cronjobs once a while 2. Data normalizaiton - often combing some data can help queries be so much faster 3. Caches - Seldom needed if you just make sure to do proper algos - and proper invalidation of caches seem to be harder than quantum physics. What "right" thing do you never do nowadays?