In software engineering, we distinguish valid ideas from false beliefs by applying the test of time. We judge an idea's certainty by whether or not people use it. Confronted by a confusing array of options for producing software, software engineers need proof of a particular approach or technique's superiority. They must know the clear-cut benefits of one approach versus another. This need to work with facts rather than assumptions is a property of any engineering discipline. Software engineering has the tools to transition from working with conjecture to working with fact. Widely using these tools will bring software engineering an important step closer toward maturity.