Systems are getting increasingly complex and it's getting harder to understand what they are actually doing. Even though they are built by human individuals they often surprise us with seemingly bizarre behavior. DTrace lights a candle in the darkness that is a running production system giving us unprecedented insight into the system helping us to understand what is actually going on. We are going implement `strace`-like functionality, trace every function call in the kernel, watch the scheduler to its thing, observer how FreeBSD manages resources and even peek into runtime systems of high level programming languages. If you ever wondered what software is doing when you are not looking, this talk is for you.