I used to agree with this, but having spent a while in a very good C++ project (by C++ standards), even if we try to always forward declare and not include any unnecessary headers in headers, we still have a clean debug build time of 30-40 minutes. Even changing a single line in a cpp file, will still take around 30-40 seconds at best with incremental builds. I think long compile times are in the eye of the beholder, but often it feels like people have just gotten used to unnecessarily long compile times because they've forgotten how fast computers are and how fast a compiler should be for most of the work except for maybe some of the more complex optimizations in -O3. It kills productivity, and should really be a much larger focus than it sometimes seems to be.