I’ve already mentioned domain knowledge several times in this book because it is critically important in data science. As a reminder, domain knowledge is knowledge that’s specialized in some way, the opposite of general knowledge. People often claim domain knowledge of an industry or a field, but someone could be a domain expert in almost anything—healthcare, the Spanish language, video game playing, seventeenth-century horsemanship, the cozy fantasy genre, farm animal management, RC aircraft, the Pokemon card game, and pretty much anything you can imagine, whether it’s a profession, a hobby, personal interests, life experience, or something else. You almost definitely have domain knowledge in several things, even if it might not be at expert level.