This WHY can be taken several ways, and we're going to explore those. The thing about motivations is that it's never just one thing, so keep that in mind as we dig into the various motivations and the different ways they can be used.
Now, the most obvious use of Defeat as motivation is Fear of Defeat. (Remember the Risk of Failure? These two are intimately linked.) You're motivated to succeed because if you don't, then Something Bad will happen.
Another motivation might be a Desire to Defeat the enemy. It's important to note that wanting to succeed and wanting to not fail are similar, but they're not the same. It's a fine line there, but it will make a difference when your characters are making those decisions in your story that can change how it ends.
Another option would be Overcoming Defeat - your character or someone that matters to them has been defeated in the past, and their goal during your story is to fix or move past that defeat, rather than avoid or inflict it.
The final option for Defeat is what I call "Indirect Defeat," meaning that it's not the Big Thing that will end everything, but it's a thing that if this one small thing fails then it can have a ripple effect. For example: your character is not trying to win the war, but is trying to hold this one outpost. The goal is smaller, but it has an effect on the Big Thing in the background that might change everything. And even within this goal within a goal, there might be yet another one (Goal Inception) with the guy that guards the postern gate that might be bribed on an important night.
Though it's not technically fiction: one of the core motivations for the story of Davy Crockett at the Alamo was Fear of Defeat (another might have been Loyalty, but we'll get into that later). How about The Lord of the Rings? One of the primary motivations for the characters throughout the book and the movies is the Defeat the Enemy.
What stories can you think of that use Defeat as one of their motivations for a character? Let me know in the comments below!
For today's Random Question of the Day:
You have been offered an Artifact that was obviously made by an enemy and has side-effects that might be very very bad at some point in the future, but the Artifact does extremely useful things.
Do you take it, and do you use it?
In the meantime, have an awesome week!