If Sarah has $50 to spend and she decides to buy a new pair of shoes instead of going to a concert, what is the opportunity cost of her decision?

The opportunity cost of Sarah's decision is what she gave up by choosing to buy the shoes instead of going to the concert. Opportunity cost is about the value of the next best alternative that she didn't choose. In this case, if the concert ticket costs $50, then that's the value of the experience she missed out on. So, the opportunity cost is not just the money spent on shoes, but also the enjoyment and fun she would have had at the concert. This helps us understand that every choice we make involves giving up something else that could have been valuable to us.