Principle / lawPerception & patterns · Cognitive Bias · Entry 128
Weber–Fechner Law – when small differences in big numbers go unnoticed
Can you tell the difference between 1 kg and 2 kg, but not between 101 kg and 102 kg? That’s Weber–Fechner Law – the difficulty in noticing small changes when dealing with large quantities.
Where it can show up
- Finance – a $10 difference feels huge on a $50 purchase but insignificant on a $10,000 deal.
- Weight & perception – gaining 1 kg is noticeable on a slim person but almost invisible at 150 kg.
- Sound & light – a small increase in volume is obvious in silence but hard to detect in a noisy environment.
A practical countermeasure
- Check percentage changes – absolute numbers can be misleading; percentages show the real impact.
- Don’t dismiss small differences – minor variations can add up over time.
- Consider the scale consciously – what seems insignificant in one context may be crucial in another.