“Know thyself” is one of the oldest ethical maxims, but it has been used to market self-tracking devices ever since the days of the humble bathroom scale. As life becomes capitalized, “know thyself” morphs from philosophical principle to profit center. No doubt specific knowledge can be gained from some forms of self-tracking, and there is much to be gained sociologically in better understanding how individuals use such technologies. But what in the long run constitutes valuable self-knowledge here—valuable for whom? The goods generated by capitalist data relations are profoundly ambiguous. They offer us, apparently, the chance to be more autonomous—in the sense of regulating ourselves more intensely—but at the cost of submitting to an external data system whose functioning requires the integration of its devices permanently into the space where, until now, we imagined we were truly, and only, ourselves.

Nick Couldry & Ulises A. Mejias, The Costs of Connection, loc. 516