A man with one watch knows the time; a man with two is never sure.
From the Murphy's law canon. Its serious form is a real problem in instrumentation and forecasting: disagreeing sources cannot be averaged without knowing which is biased.
In practice
- A ship carrying two compasses three degrees apart must choose which to steer by, and averaging them is a decision rather than a solution.
- A company with two dashboards reporting different revenue figures has less usable information than one with a single imperfect figure.
- Further reading
- Wikipedia
- Subject
- Decision-making & Reasoning
- Essay
- Paradoxes that broke theories, and sayings that outlived them