The philosopher Nick Riggle is only in his forties, but he seems to have lived enough for many lives. He dropped out of high school to become a professional skater, pioneering the playful, dance-like form known as “mushroom blading”. He competed in the X Games and hung out with Randy Savage, Woody Harrelson and Eminem. He had a mystical experience of oneness with eternity and became adept at meditation. He recorded an album as the lead singer of a folk/hip-hop band. And he is a now a professor at the University of San Diego and a brand-new father.

Riggle is also the author of a lyrical new book, This Beauty, about what he calls “the Question”. Given that we never asked to be born or consented to our own existence – having been “abducted from nowhere”– why should we embrace our lives in all their unpredictable mystery? It’s a question that gripped him for the first time when he “woke up” at the age of thirteen, but it is freshly prompted by parenthood, and the audience for his book includes his infant son. For Riggle the Question is personal.

His strategy for answering it is refreshingly off-beat: to scrutinize the life-affirming clichés of pop culture, the words of those for whom the Question has been settled. You only live once! Seize the day! Live in the moment! Riggle calls these phrases “existential imperatives” and he investigates them with generosity and deadpan wit.

He spends most time on “YOLO”– you only live once – tracing the idiom from Goethe’s play Clavigo, where it is used to justify competitive social climbing, to Drake’s song “The Motto”, which coined the now tired acronym. (“I sincerely apologize”, Drake said in a recent television appearance. “I did not know your annoying friends and co-workers would use it so much.”)

This brief history casts doubt on the wisdom of YOLO. If the slogan tells us to take risks, isn’t that frequently bad advice? Riggle recounts the grim anecdote of a rapper who tweeted “YOLO” while driving at 120mph, just before a fatal crash that killed everyone in his car. On reflection, though, it isn’t clear why YOLO favours risky behaviour. Why not react instead like Riggle’s “Preservationist”, who jealously protects the only life he has, as we safeguard other rare and valuable things? “There is only one precious, irreplaceable Stradivarius guitar in the world”,...