Weber–Fechner law

Perceived difference is not the same as actual difference. We think 10 to 20 is a bigger change than 1000 to 1010.

Consequences

Weber–Fechner law can explain the increasing levels of public expenditures in mature democracies. Election after election, voters demand more public goods to be effectively impressed; therefore, politicians try to increase the magnitude of this "signal" of competence – the size and composition of public expenditures – in order to collect more votes.