It seems obvious on first inspection. We buy things because we need them. Yes, and no. Certainly the need (or perceived need) for a product, combined with the supply, is what creates the conditions for an exchange to occur.

Every purchase is an exchange. An employee exchanges time for money. A retailer exchanges inventory for money. Someone using barter may exchange wheat for berries. In every case there is one thing in common.

The two parties have a different valuation of the same thing!

Without this different valuation, the exchange would not occur. The employee values the money more than the time (maybe he could use more money for his time, but couldn’t we all …) The employer, on the other hand, values the employees time more than the money! Same amount of money, same amount of time, different valuation depending on perspective.

This is true for every voluntary exhange. All of the above exchanges are voluntary. No coercion or threats are necessary, just a different perspective on value.