Like many technologists, I assumed outcomes without fully testing my changes. I see this is over and over again, and I encourage my team to "try it out" or "show me" or "ask". Because developers work in a virtual world, they extrapolate and make assumptions about their code/config changes, its their MO. Because managers work in the real world, they need to check these assumptions. Does your new printer work? Is the new blackberry working same as old? Can you access that directory now? Is date range on that report query what you needed? I have an adage that it doesnt work until it's been observed to be working.
Test-driven development is a great step towards getting developers to test their assumptions, but many businesses could improve with a test-first CTO.