The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that whe... — Douglas Adams

The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at or repair.

Author: Douglas Adams

Insight: There's a sneaky paradox in how we think about reliability. We design systems with so much redundancy and fail-safes that we convince ourselves they're bulletproof—until they break. Then we discover the crucial component is buried three layers deep, behind something else, accessible only if you disassemble half the machine first. The confidence itself creates the problem. This shows up everywhere. Your phone's battery is glued in because the engineers deemed it impossible to fail. Your car's computer is tucked in a spot that costs $800 in labor to access. We optimize for sleekness and efficiency by burying complexity, then act shocked when a minor hiccup becomes catastrophic. The things we're most certain about are often the things we've least prepared to fix. The real lesson isn't to distrust confidence—it's to stay suspicious of it. Simple, accessible systems might look less impressive, but they're forgiving. They fail loudly and visibly, and you can actually do something about it. When we design for "impossible to go wrong," we're often just designing for "impossible to fix when it does."

Source: Mostly Harmless, p. 127, 1992