 To understand this proposal, let’s begin with incompletely realized activities. These are activities one engages in when one learns X “by doing”: e.g., a novice piano player learns to play by slowly reading simple note sequences and pressing (at least some) corresponding piano keys, guided by the end of mastering the instrument. With certain background conditions in place, the pressing of the keys is best thought of not as playing the piano badly, but rather as incomplete realizations of what piano playing amounts to. Jaworska and Tannenbaum interpret certain activities of cognitively unsophisticated humans analogously. With certain background conditions in place, when a child or a cognitively impaired adult models, even in a most rudimentary way, a cognitively sophisticated activity, guided by a mentor’s (parent’s, caretaker’s) end of the mentee acquiring cognitive sophistication, the mentee incompletely realizes the corresponding cognitively sophisticated activity. For instance, playing a simple game like “I-smile-then-you-smile” becomes rule following as an incomplete realization of practical reasoning.