According to Greek myth, Achilles' goddess mother dipped him into the River Styx to make him invulnerable to injury, but the heel she held him by wasn't dipped. As fate and story would have it, he died when someone shot him in that heel.
Most people and the most interesting fictional characters always have an Achilles heel, that one weakness which will defeat them unless they overcome it.
As a writer, you must figure out what your main character's weakness is and attack it through plot.
That weakness can be fear of some physical danger. If like Indiana Jones, your character is afraid of snakes, then snakes he must face to achieve victory.
A better weakness is an inner one. If your character prides himself on his dignity and fears ridicule, he must find the strength, at his high school reunion, to race across the room in his bunny underwear to protect his girlfriend from the same bullies who just stripped him.
If he fears death, he must find the strength to risk dying for something or someone who is more important than life.
Minor weaknesses and disasters can add conflict to a scene, but that one Achilles' heel of your character and his attempts to overcome it are the heart and soul of a good story.