The Mechanics Behind Want Vs. Need
The difference between the two lies within the concept of justification.
When one first approaches story structure, they become introduced to the concept of a Hero's wants clashing with what he or she truly needs. As useful as this tool can be in analyzing a story after the fact, it is what lies beneath it that is of import to an Author.
No matter where you look, the idea of want vs. need persists:
[Heroes] do greater and greater things to get what they want, take more and more extreme measures to achieve this goal, until, perhaps, they turn a corner, and we're no longer rooting for them – we realize that [to] achieve this WANT, without servicing this NEED would be worse than never having what we wanted in the first place…the hero realizes it too
This particular explanation comes from Million Dollar Screenwriting instructor Chris Soth, but is exemplary of the thinking behind a Hero's internal struggle towards the end of a story. The Hero wants something, strives for it, but near the end of the 2nd act discovers that what he wants doesn't match up with what he needs. He ditches his original motivation for this new one, and marches into the 3rd act with a new purpose.
What did Robert Angier need in The Prestige? He wanted to be the greatest magician the world had ever known, even if it killed him. Need? If anything he needed the adulation of the crowd more than he wanted it. Contrary to the above understanding, his unconscious need syncs up perfectly with his conscious want. Same with William's need/want of a free Scotland, Salieri's need/want of being remembered way past his years, and Ree's need/want of finding her missing father.
Is there an explanation for this dissonance?
The Mechanism That Is Justification
The concern with this second group of Heroes stems from the fact that they are all "teaching Heroes" who don't change. Instead of discovering some deep-seeded personal problem that they were unaware of, these characters find themselves driven to focus on solving the problems external to them. Because they are aware of what drives them, these Heroes will turn to it as a source of motivation to get them through their story. Act by act they build up a reason to justify their actions during the moment of crisis.
The other group of Heroes, the so-called "learning Heroes" start out with that psychological justification intact. In these cases, each Hero's story becomes a process of revealing this justification to them. Luke was unaware that he had this huge chip on his shoulder that compelled him to test his mettle against everyone he met. Ben revealed this to him, giving him a reason to trust something outside of himself.
Interestingly enough, Will Hunting had the same exact chip on his shoulder. Anyone but his closest friends became instant fodder for his rigorous scrutinizing--a result of Will’s parents abandoning him at such a young age. Through his relationship with Sean (Robin Williams), Will became aware of this problematic tendency, and like Luke, found peace through a willingness to trust others.
One group of Heroes undergoes the process of justification, the other has their justifications revealed to them. Both are attacking a problem. One happens to be looking in the wrong location.
Final Resolve and What It Means
In both cases, the Heroes have the same decision to make at the end of a story: continue doing things the way they always have or adopt a new approach. For the Hero that changes, they are solving their internal problem--their source of grief. That is why from the outside (the audience's perspective), it looks as if they are fulfilling a need. Most Heroes want to be free from their grief. Only once revealed to them what they "need”, do they then find it.
For the Hero that simply soldiers on, they started out motivated by this need. Revealing it to them will have little to no effect on them. Instead, when it comes to that crisis decision, they continue to focus their efforts where they always have--on working the problem.
Regardless of their final resolve, what they want or seem to need, Heroes showcase a particular approach to problem-solving.
Why Want vs. Need Doesn't Work
Screenwriter John August on want vs. need:
I spent a few hours this week looking at the characters in my project through the want-vs-need lens, before finally concluding it is complete and utter bullshit. Trying to distinguish between characters’ wants and needs is generally frustrating and almost universally pointless. The fact that I can answer the question for Big Fish and Charlie after the fact doesn’t make it a meaningful planning tool.
The reason why want vs. need fails for creative writers is because it is an interpretation of meaning after the fact. Much like the dueling concepts of learning Heroes and teaching Heroes, these interpretations of a story's events spring forth as the credits roll. The concept functions after the first draft or two as it makes the final message concrete, but is that helpful when staring at a blank page?
When setting sail on a work of narrative fiction, the drive should be there to say something meaningful with the story. If it isn’t, then the Audience on-board can expect a ride adrift a pointless and hollow sea.
If, on the other hand, the intent is to communicate something profound, then understanding the process of justification and how it works with the central character of a piece remains the best practice for righting the rudder.
Advanced Story Theory for This Article
While the focus of this article is on the Hero, the uselessness of want vs. need applies to all Main Characters. When people speak of a Main Character's want, what they are describing is the Main Character's Response. Luke wants the waiting to End: the waiting to join the Academy, the waiting for his Jedi training to end, and so on. These apparent problems are Focuss of his real problem of Test. Likewise with Will you have a Main Character focused on the Cause for his genius as one of the reasons why he can't get close to anyone. He looks at a piano and sees black and white keys and a box of wood--the same way "regular" people look at high-level math. These are simply Focuss, the distancing Effect he fosters on others is growing from his true problem of Test.
When people speak of a Main Character's need, what they are describing is the Main Character's Solution. Both Luke and Will need to start Trusting. From the Audience's perspective the only way the Main Character succeeds (and this is assuming a Judgment of Good) is when they do what they "need" to in order to overcome their own personal Problem. But this only works smoothly in Changed Main Characters.
The reason "need" breaks down in Steadfast Main Characters is that their solution is never employed. Why? Because if they were to make that switch, they would lose all motivation to end the story. Their original drive (a Steadfast Main Character's Problem) would lose its power. Steadfast Main Characters that use their solution cancel the argument for want vs. need.
Warping The Prestige into the concept of want vs. need finds Robert Angier "needing" the Ability to perform the Transported Man. He achieves this, so then what? What does that mean? The fact is want vs. need doesn't say anything meaningful about story, which is another reason why it fails. It's far more meaningful to think of Angier's Steadfast drive of Desire and how that ended up in a Personal Tragedy.
With the combination of Resolve, Outcome and Judgment an Author has powerful tools to craft meaning.