Imagine that after having packed a large suitcase, you want to add an item. You can just throw it in. No item needs to come out. You do not need to rearrange the contents because the suitcase had extra room to begin with—it had slack. But with a smaller suitcase, adding something necessitates taking something out. Slack is what allows us to feel there is no trade-off. Where does the money for the $10 cocktail come from? If you are well off, the cocktail will feel like it comes at the expense of nothing because in a way it does. Slack picks up the tab. Slack frees us from making trade-offs.
