Researcher Stuart Brown says that play isn't important to children, it's important to humans (or for that matter, all high functioning animals). The broaden and build behaviors it fosters may have even greater value for adults than children. The mental state of flow is also a major component of play, and has itself been associated with things like creativity and happiness. Brown often quotes Brian Sutton-Smith's insight: "the opposite of play is not work, it is depression."[17] Examples of adult play abound (e.g. the arts, but also curiosity driven science).

Tim Brown explains that values like a bit of shamelessness during the creative process is extremely important in adult designers.[18]

Play may allow people to practice useful habits like learned optimism, which might help manage existential fears. Play also offers the opportunity to learn things that may not have otherwise been explicitly or formally taught (e.g. how to use, and deal with, deceit and misinformation). Thus, even though play is only one of many habits of an effective adult, it remains a necessary one.[10]