Scarcity forces trade-off thinking. All those unmet needs capture our attention and become top of mind. When we are tight on cash, we are highly attentive to all the bills that must be paid. So when we consider buying something else, all the bills are there, making the trade-off apparent. When we are working on a tight deadline, all the things we must get done are foremost on our mind. So when we think about spending an hour on anything else, the trade-offs again are salient. When time or money is not so tight, we are not as focused and the trade-off is less apparent.
