Is “Defensive Programming” actually healthy?

I can’t solve this one, and I think I need your help. So, a developer was responding to a code review comment I made and they simply asked me, “why would I do that?” I gave my standard, dusty answer: “because you have to code defensively— you don’t know what the future holds.” But I suddenly realized… am I proliferating a fear of the future? How could I code fearfully when I run CubicleBuddha.com where I blog so often about living happily in the present? I’ll share the specific code example with you. I’m hoping to hear from the community whether my solution is “coding in the moment” or if I am actually bowing down to the fear.