We naturally follow a “what’s in it for me” law in everything we do, be it the pursuit of a hobby (fun overweighs the cost), a job (money overweighs the effort) or an investment (gain overweighs the risk). Even if we’re not aware of it, we’re always performing this comparison in our minds, and logically assume and expect others to do the same.
The good ol’ gain over cost estimation that drives our modern world is also valid for fictional worlds. We expect fictional characters to have the common sense to make profitable choices, otherwise they lose credibility. If they make poor choices without good reason, we nturally assume they’re a bunch of boneheads, and we’d be right. So, as writers, we must learn to make good feasibility studies whenever we plot our stories.
Feasibile means capable of being accomplished or brought about. In other words, realistic. A feasibility study is an analysis and evaluation of a proposed project to determine if it is (1) technically feasible, (2) feasible within the estimated cost, and will later be (3) profitable. In other words, possible, affordable and worthwhile.
When they want something, people intuitively performe a feasibility check and choose the path of least resistence to get the thing they’re after. Sane people will always opt for the course of action that is easiest, least costly and least risky to reach their goals. And your characters should do the same.
Since you’re a writer, you’re probably a sadistic little bastard who loves to create lovable people, bestow them with all that’s good and nice in the world, and then plop them into chaos and watch the squirm and writhe in their own despair. I know I do, and I love it. But just because we like to make our characters’ lives miserable doesn’t mean they should make things complicated for themselves.
If your protagonist has a goal that he wants to reach, he’ll look for the shortest way to reach it. You will put obstacles in his way—or better yet, the antagonist will put obstacles in his way—but he’ll always look for the easy way out. Your protagonist will never opt for a convoluted solution to his problem if he can pick a simple one. He won’t be looking for ways to give as much as possible, risk as much as possible and alter his personality just to cross the road and get a bagel.
So remember, when you send your protagonist forth into the mighty adventure of Storyworld, make sure you run a feasibility study on his choices and actions. Make them smart and sensible, and feasible within your story. Nobody wants to relate to a thickhead, not even a fictional one. And you don’t want your readers to watch some dude heroically jump the barbed-wire fence with the gate wide open, now, do you?