At any moment in time, there is a limited amount of cookies in existence. Economists study what to do given the fact that there is a finite amount of noms to go around. Many of the problems humans face can be explained in terms of “scarce resources.”
There will always be a finite amount of stuff, but in the last 150 years the total size of the human economy has grown. Pretty incredible ->
GDP per capita is a rough measure of how much stuff the average person is producing (and therefore consuming) in a year.
The “economic pie” is a term for how much stuff there is to go around in a society. The economic pie has grown significantly in the past few centuries. So a lot of people have more healthcare, shoes, and most importantly cookies.