Nietzsche said, "He who has a why can endure all the hows." Without meaning, life is reduced to a repetitive mechanism. Routine empties the everyday of this "why," it automates existence. Routine is deadly not biologically, but spiritually and psychologically. We become spectators of our lives, rather than actors.
Coelho's phrase is based on a universal tension: Routine symbolizes security and predictability. There is an apparent comfort in it: no risk, no surprise, and therefore no fear. But this comfort becomes a gentle prison, which ends up stifling the vital impulse. It is a slow death: that of dreams, curiosity, passion. Adventure symbolizes uncertainty, change, risk, but also the possibility of being fully alive. It involves stepping outside the known, and therefore confronting fear, but this is where truly transformative experiences are found.
Here we can see a resonance with existentialist philosophy: to live is to choose, to engage in the unknown, even if this means confronting anxiety.