Signal-to-noise ratio
From Kevin O'Leary on The Diary of a CEO
Signal-to-noise ratio (SNR) is a measure of how much useful information (“signal”) there is relative to irrelevant or unwanted stuff (“noise”). It originated in engineering — in audio or radio, it’s literally the ratio of the power of the signal you want to the power of background interference, usually expressed in decibels. A high SNR means a clean, clear signal; a low SNR means the signal is drowning in static.
The concept has spread far beyond engineering because it’s such a useful metaphor.
In data and analytics, signal is the real underlying pattern (an actual change in user behavior, a genuine effect of your feature), and noise is random variation (day-to-day fluctuation, seasonality, small sample sizes). A metric with low SNR moves around a lot for reasons that have nothing to do with what you did — which is exactly why A/B tests need enough sample size: you’re trying to lift the signal above the noise floor.
In communication and writing, signal is the content that actually informs or persuades, and noise is filler, hedging, jargon, or tangents. A high-SNR case study or email says a lot per word.
In product decisions, signal might be consistent feedback pointing at a real problem, while noise is one loud customer or an anecdote that doesn’t generalize.
The practical takeaway is usually one of two moves: amplify the signal (better measurement, clearer writing, bigger samples) or reduce the noise (remove confounds, cut filler, filter out unreliable inputs). Anything that improves either one improves the ratio.
Signal-to-noise in people
The metaphor even gets applied to people. In a clip from The Diary of a CEO, Kevin O’Leary — who dealt with Steve Jobs directly for years — describes Jobs as 80% signal, 20% noise, and Elon Musk as 100% signal. His definition of signal there is worth keeping: the three to five things you must get done in the next eighteen hours; everything that stops you is noise. The percentages themselves aren’t measurements — nobody instrumented anyone’s attention, and “100%” is hyperbole — but the framing turns focus into the same two moves as everywhere else: know what your signal is, and cut what isn’t.