Writing high-performance software these days is a challenging task. Today's hardware ecosystem is highly heterogeneous, with a trend towards application-tailored solutions. Despite years of effort in automation, by and large the burden still falls on the developer to write a program in a manner that can take advantage of this hardware. Oftentimes, the solution is to use a library carefully written by a performance engineer for the specific combination of application and hardware. But why is that? What happens when there is no library?