Eat five portions of fruits and vegetables a day. Walk 10, 000 steps. Drink eight glasses of water. Sleep eight consecutive hours a night. These magic numbers are meant to keep us healthy. In order to optimize our well-being, smart apps track our hydration levels, our intake of greens, our sleep and, of course, our every step. Yet, supposed benefits aside, these targets have one thing in common: They all have their origins in marketing strategy—and in one case, a This story is from Kinfolk Issue Thirty-Five Buy Now Related Stories Arts & Culture Issue 47 Correction: The Starving Artist Bad times don’t always make for good art. Arts & Culture Issue 45 Correction: Spontaneous Generation A curious theory about the origins of life. Arts & Culture Issue 44 Correction Wikipedia is good, actually. Arts & Culture Issue 40 Correction On the scary shortcomings of “fearless” philosophies. Arts & Culture Issue 39 Correction Teenagers aren't lazy, they're exhausted. Arts & Culture Issue 38 Correction Don’t be fooled by spurious data.