Money Illusion

Money illusion is the psychology of judging by money's 'nominal amount' alone, without adequately reflecting changes in prices. You're fooled by the number itself and miss that money's actual purchasing power.

The economist Irving Fisher framed this concept in 1928 as 'the failure to perceive that the value of the monetary unit rises or falls.' Later, in 1997, Shafir, Diamond & Tversky presented experimental evidence that people really do fall for this illusion.

'Nominal' is the amount as the number reads, while 'real' is value measured by the actual quantity you can buy, reflecting changes in prices.

As in the earlier example, if your salary rose 3% but prices rose 4%, that's +3% nominally but roughly -1% in real terms. The number in your account grew, yet the goods you can buy shrank. Conversely, a 3% raise in a year when prices barely rose is close to a real gain too. The same '3%' means something completely different depending on inflation.

The same trap exists when you look at investment performance. It's easy to be pleased that 'my assets grew 20% over 5 years,' but if prices rose by as much over the same period, your actual purchasing power may be nearly flat.

In particular, assets whose nominal amount doesn't shrink — like bank deposits — feel 'safe,' but if the interest is lower than the inflation rate, the real value quietly declines. You simply lack the sense of taking a loss because the principal stays the same. So in long-term investing, you have to measure performance by real return, not nominal return, to see the true picture.

The way out of money illusion is simple: whenever you look at a return or a raise, also recall 'how much did prices rise over that time?'

If you use 'can I buy as much as before with that money' as your standard rather than 'by what percent did it grow,' you fall less into the trap of nominal numbers. Remember that an asset that fails to beat inflation over the long run is losing value in real terms even as the number grows.