Understanding Media by Marshall McLuhan. He is most famous for remarking that "the medium is the message."

The media we use influence the way we think, the way we act, the political narrative of our times, etc. by placing limits and incentives on the messages we convey through those media. As an easy example, consider Twitter: you cannot have a coherent and intellectually involved conversation on Twitter. If Twitter were our only method, or main method, of communication, that property would drastically shape public discourse.

As technologists, we are developing the communications media of the future; it is imperative that we take on this task responsibly by first reflecting on the design and effects of media from the past.