Back in the late 19th century some economists had a revelation that what if we look at the economy with a different lens rather than looking at it through the lens of social classes.
Individuals make choices because of their preferences the neoclassical economists introduced marginalism the idea that value comes from the additional or extra satisfaction you get from consuming one more unit of a particular product.
Their Theory view people as rational actors who make decisions to maximize their satisfaction given their limited resources therefore businesses aim to maximize profits while consumers aim to maximize utility and prices act
Now think about eating chocolate the First bite has an amazing and really great taste and each time you chew it you want more and more of it as a matter of fact you can't get enough of it
But here's where everything changes the fourth bar becomes less exciting and by the time you get to the last chocolate bar you might even pay someone to take it away or give it out because you have simply had enough and it's no longer appeasing
This is simply diminishing marginal utility which explains why water is essential for life but it's cheap while on the other hand Gold which we can live without is expensive. The more something is available the more its additional satisfaction diminishes and it becomes valueless.
The Neoclassical economics revolutionized how we think about value and price unlike Adam Smith classical or Karl Marx marxian economists who view value in the form of labor.