Some knowledge is hard to write down. Imagine trying to teach yourself karate from books only. It might be similar with some mechanical or artistic skills that

Some knowledge is hard to write down. Imagine trying to teach yourself karate from books only. It might be similar with some mechanical or artistic skills that are best taught in person. Arguably, nowadays, with cheap recording devices everywhere, it is easier than before to produce comprehensive documentation even for such activities that are hard to write down.