The most dangerous words in engineering and in life are “always” and “never.”

The trap

Rules feel safe. “Always validate input.” “Never skip tests.” “Always prefer composition over inheritance.” These heuristics exist because they encode hard-won experience, and following them blindly is usually better than ignoring them entirely. But the people who formulated them didn’t mean them as absolutes — they meant them as defaults that apply under certain conditions, and those conditions don’t always hold.

When you treat a conditional rule as an unconditional one, you stop thinking. You apply the rule in situations where it actively causes harm, and you defend it with “that’s the rule” instead of “here’s why.”

The pattern

Every meaningful rule has implicit conditionals attached:

  • “Always validate input” — when it comes from outside your trust boundary
  • “Never skip tests” — when you’re not in a throwaway prototype or a read-only migration script
  • “Prefer composition over inheritance” — when the shared behavior isn’t a true is-a relationship

The rule isn’t wrong. The unconditional application of it is.

Epistemics

This applies beyond engineering. Every belief you hold is conditional — conditioned on your evidence, your context, your priors. The most rigorous thing you can say about almost anything is not “X is true” but “X is true given what I currently know, under these assumptions, in this context.”

That’s not relativism. It’s precision. “Everything is conditional” doesn’t mean nothing is reliable — it means reliability itself has conditions, and knowing those conditions is part of knowing the thing.

In practice

When someone states a rule as absolute, ask: under what conditions does this break down? If they can’t answer, they don’t fully understand the rule. If they can, you’ve learned where the real reasoning lives — not in the rule, but in the conditions that constrain it.

The goal isn’t to find exceptions to everything. It’s to hold rules lightly enough that you can recognize when you’ve left the domain where they apply.