Ask HN: Is the full stack developer more myth than reality?

One of the original selling points of NodeJS was that one developer could apply the same language in front and back, making the Javascript skillset more valuable to an organization as resource demands shift among projects. Yet, considering the demands of both frontend and backend development, it seems unlikely that one person would change that often, if at all, because of comparative advantages due to domain expertise. What can people from HN report on this experience in the wild-- is the full-stack developer more myth than reality?