I was so bored of being bed-ridden at the hospital that I eventually started browsing the source code of a C++ game engine (Irrlicht engine) and use that as documentation for a small game project. During that experience I learned to read the local documentation, read the source code and actually figure out how stuff was implemented in the engine, which quirks it had and even modify and recompile it.
Simply because I was bored and I had no way to get the answers I needed off the internet.
It was a very enlightening experience, I think every developer should get to a point, at least once in their life, where they're just sitting in front of the computer with no external distractions and no internet connection, just explore what you have and make the best out of it.