"... You've got to stand for something, or you'll fall for anything ..."

We tend to try to satisfy our desires by the degree of intensity and scarcity in which we as individuals view them at any particular time. 

We will then seek to satisfy our scarcities (needs or desires) by giving up (exchanging) some of what we have in surplus (value less) at that particular moment.

So what is a scarcity, and what is a surplus?  These are constantly varying and changing for each and every person.

As we acquire things or satisfy certain desires, we tend to value somewhat less further acquisitions of the same thing.

For example, a man may want one home, one automobile, one hat, or one walking stick.   Another man may want two homes, three cars, no hats, and no walking sticks.

Clearly the second man perceives a greater value in owning multiple homes and cars, and percieves no value at all in owning either hats or walking sticks. 

He will likely pay great sums of money for his houses and his cars, but will probably not spend so much as a dime on either hats or walking sticks.