Needs and wants are often split into two distinct, and sometimes conflicting, categories. I propose that these two categories intersect, and should ideally overlap entirely. It is easier to see why someone should want what they need. If a person does not want what they need, they make choices that are detrimental to some aspect of their health. For instance, if I do not want to eat vegetables, I might maintain a diet that lacks the necessary nutrients. Therefore, it is important to want the things that we need so that we will choose them.
The other intersection is a little more complex to explain. If a person wants something that they do not need, it may be an indication of discontentment, but not necessarily. I would argue that at the root of any desire is a true need. C.S. Lewis writes in Mere Christianity:
The Christian says, ‘Creatures are not born with desires unless satisfaction for those desires exists. A baby feels hunger: well, there is such a thing as food. A duckling wants to swim: well, there is such a thing as water. Men feel sexual desire: well, there is such a thing as sex. If I find in myself a desire which no experience in this world can satisfy, the most probable explanation is that I was made for another world. If none of my earthly pleasures satisfy it, that does not prove that the universe is a fraud. Probably earthly pleasures were never meant to satisfy it, but only to arouse it, to suggest the real thing. If that is so, I must take care, on the one hand, never to despise, or to be unthankful for, these earthly blessings, and on the other, never to mistake them for the something else of which they are only a kind of copy, or echo, or mirage. I must keep alive in myself the desire for my true country, which I shall not find till after death; I must never let it get snowed under or turned aside; I must make it the main object of life to press on to that country and to help others to do the same.
If I want something, I should ascertain whether or not there is a true need and what the correct fulfillment of that need is. Choices proceed from wants, and wants proceed from values. If our values do not proceed from the innate needs that God instilled in us, we will inevitably make decisions that are detrimental to our health and leave us discontented.