There are some things you can learn from a book or video - like how to make sushi, the history of Puerto Rico, or the varying methods for valuing a company. I'd argue that there are other things - like leading a team, comforting others, or making decisions in a crisis - that can only be discovered through experience. I'd argue further that the most important skills for having a good life can't be learned from a book. 

It stymies me that reflection isn't a cornerstone of every learning enterprise on the planet.

Reflection is the key that unlocks tacit knowledge, the type of knowledge that can only be discovered through experience. Acquiring tacit knowledge is different than learning from a book because it takes more than memorization of the mind and body. Instead, it takes having new experiences, failing or succeeding, and internalizing what you learn. Tacit knowledge doesn't stick if you don't internalize it, and that internalization only happens through reflection.

Ironically, reflection is something that can be learned from a book or video and practiced. For a reason unknown to me, it just doesn't seem important enough to make part of the core body of explicit knowledge we learn in school. I think that's a monumental miss.