We have developed an entire science of failure, but very little literature exists on why systems work. While failures are dissected and catalogued through post-mortems and crash reports, success remains largely unanalyzed. Given the imperfection of everything we build, one can’t help but wonder why they can work at all. Every engineered artifact—from aircraft and reactors to the electronics on a lab bench—operates under a hidden choreography of flaws, variances, and latent defects. This chapter explores the paradox of reliable function emerging from unreliable parts, the hidden probabilities that keep our machines alive, and the interplay between complexity, reliability, and human error.