If you put it in a mattress, sure.

But most (all?) people invest their money at a far higher rate of return than inflation.

Not for a decade or more has this been true. Inflation in the UK is 2.2%. You would be lucky to get that without venturing into equities (which to be fair have done well this year) or property. But energy is up 8%, travel 9%, food 12%, etc. Real inflation is hard to outrun. And markets are prone to bubbles...