Give your protagonist a hard time. Not because you should behave like a sadist but because conflict and adversity are what drives your story along.
If, for example, you are writing the script of a Road Movie in which your protagonist travels from Chicago to Los Angeles and nothing bad happens to him the whole way, then that would be one very boring movie. If, on the other hand, he were chased by a mad trucker, shot at by bikers and blown up in a diner, that would be more interesting.
Give your hero a worthy antagonist and make things look hopeless for him. Put obstacles in his way. If it looks like he’s about to succeed at something, snatch it away before it can happen.
Pile on the pressure from outside. If your hero is unjustly convicted and on the run, make ordinary, law-abiding citizens his enemies. Children should tell on him, people he thinks of as friends must give him up to the law.
And nature should play its part. If he’s hiding out, turn the night-time temperature down to minus ten. Blow away his shelter. Soak him in torrential rain. Poison his water.
The tougher things are for your hero and the tougher the opposition that faces him, the better your story will be.
Your hero should bend under the insurmountable odds that face him. All his strengths and skills must be stretched to breaking point. But he must never give up – at least, not for long.
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