Custom answered these questions in previous times, but just as technology has transcended its former limitations, we seem less moved by the imperatives of tradition. At one time, tradition set limits on where people could be intruded upon and when. Even with the necessary technology, it was not always so easy to reach people in their homes, let alone while walking or in a taxi. For the majority, religious practice used to define certain inviolable spaces and moments. Less formal norms, like the time reserved for family meals, exerted considerable force as well. In this world, privacy was the default, commercial intrusions the exception.

Tim Wu, The Attention Merchants, loc. 1138