Challenge: systematically question why things are done the way they are

Ask "Why must this be this way?" for each element of the problem — not to be contrarian, but to find which constraints are real.

Why it works

Problems persist partly because assumptions about constraints become invisible. Once an assumption enters the standard approach, it stops being examined and starts being treated as a physical law. The challenge technique makes the implicit explicit: by systematically asking "Why must X be true?" it separates historical convention from genuine necessity, revealing the subset of constraints that are actually inviolable and the larger set that are not.

How to do it

1. List five to ten elements, assumptions, or features of the current approach to the problem.
2. For each, ask: "Does this have to be this way? What would happen if it weren’t?"
3. Categorize: which constraints are physically necessary, which are legal or regulatory, and which are just convention?
4. Treat the convention-only constraints as candidates for deliberate redesign.

Evidence

First-principles reasoning — examining which constraints are real rather than inherited — is a documented element of expert creative problem-solving in engineering and design. De Bono’s challenge technique is a systematic delivery of this in a non-technical frame. (mechanistic)

First-principles reasoning is discussed extensively in engineering and design literature but the specific "challenge" technique as described by de Bono has not been isolated in trials.

Common mistake

Using the challenge as adversarial critique ("this is dumb") rather than genuinely exploratory inquiry — the goal is to find which constraints are real, not to dismiss everything.