zero

people must (and want to) consume in order to do so, people must also produce. people dont always want to produce the same things they consume some people have a greater ability (and/or willingness) to produce things than others

so lets assume a system where different nodes (ppl/groups of similar people) are somewhat specialised in the thing they produce now people can trade a thing they've produced (but dont require) with another node that has something they want to consume

this becomes hard, because things some things are more 'expensive' than others. they take more time, more resources also, the other producers whose product i want to consume, might not want MY product at all this is where we need a way of quantifying or evaluating products