However, take some of the science positions in the book with a grain of salt. The author is notorious for being directionally correct in his opinions, but exaggerating a lot of the science for dramatic effect. This doesn't matter at all if you're reading the book to convince yourself to build better sleep habits, of course.
However, it does seem to leave some people with exaggerated worries or anxiety about dying early or developing serious disease conditions if they've ever gone through periods of life with short sleep (college, raising kids, video game addiction) or if they're in a life situation that limits their sleep. In that regard, it's worth noting that the author is really stretching some of the studies and cherry-picking results to support his argument. Getting 6 hours per sleep at night will not be the death of you, despite what the book suggests.
It's also commonly known that people get less sleep than they think they do. Someone might tell you they get 8 hours of sleep each night because they try to sleep from 11PM to 7AM, but in reality they stretch their bed time to midnight more often than not and then read their phone in bed for 15-30 minutes. Sleep advocates try to compensate by exaggerating target sleep times for adults to 8 hours. In reality, 7-ish hours of sleep appears to be just fine for most adults, with some requiring less and others requiring more. That said, most people will have to target 8 hours of dedicated bed time to really get those 7 hours of sleep in practice, hence the common exaggerations.