Like any 21st century pop science author, the premise of a long book about sleep couldn't be a down-to-earth argument of marginal health improvements. Instead, it doubles down multiple times on how this has to be, "undeniably", the most important yet neglected health knowledge ever - a common recipe for best sellers, promising immense rewards for memorizing a few key concepts.

Stripped down of the obvious marketing strategy, the over-the-top framing and all the speculative fluff mixed in with the actual research data, the book does a good work on hammering the need of caring for our sleep. And like any book of its kind, in the end the advice is as predictable and close to common knowledge as one would guess:

1) Go to bed and wake up at the same time every day; 2) Exercise at least 30 minutes, not too close to bed time; 3) Avoid caffeine and nicotine after noon; 4) Avoid alcohol before going to bed; 5) Avoid large portions before going to bed; 6) Avoid medicines that delay or disrupt sleep; 7) Don't take naps after 3PM; 8) Relax before bed; 9) Hot bath/shower before bed; 10) Dark & cool bedroom, no screen devices; 11) Get morning sunlight every day; 12) Don't lie in bed awake;

Most annoying of all, no concrete answers on "why we sleep". Walker presents some speculative argumentation regarding what fits an evolutionary and utilitarian viewpoint, but very little evidence is available anyway and, most worryingly, zero counter-evidence or opposing research viewpoints are discussed. In the end, the answer currently available is as obvious as the 12 advices above: because it's good for us.