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- All performance measurements are initially bad: bugs in the measurements, not measuring what you think you are measuring, and bugs in the system
- Biggest danger: initial measurements look good, so you don't bother to figure out whether they are even correct
- If there is anything about a measurement that seems even a little suspicious, distrust everything until you explain it; it's possible that there is an error that has skewed all of your measurements.
- Find multiple ways to measure each key result, and make sure they are consistent
Measure one level deeper
- To understand performance at one level, you must measure the constituent factors that explain that performance; you should only trust a result once you understand clearly why you are getting that result
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