The crucial part of any successful story is conflict.
The conflict represents all the problems that are appearing on the hero’s journey towards reaching her goal.
Conflict is not purely two people yelling at each other or fighting.
Conflict can be internal and external.
Internal conflict represents all inner struggles that a character can have ( insecurity, self-delusion, anxiety, regret, fear, motivation, discipline, etc).
It is usually represented by the hero’s thoughts. Sometimes it’s hidden and simply assumed by hero’s reactions and actions or lack of them.
Namely, inner conflict is whatever is preventing the hero to reach her goal and it’s coming from the hero herself.
Unlike internal conflict, external conflict comes from the outside world.
The source of the conflict can be another character, group of characters, institution, and a natural or a supernatural phenomenon.
The conflict between characters can be achieved by them wanting the same thing (usually two or more characters want to win or possess something or someone).
The characters may desire entirely different things (a man wants to have a baby, but a woman doesn’t want).
A character can be simply standing in the hero’s way (like a gatekeeper).
The hero can be in conflict the justice system or educational system or family but all these systems are better represented with a single character (a corrupted judge, crucked policeman, crazy teacher, pushy parent, etc).
The hero can be challenged by a natural phenomenon (hurricane, tsunami, fire, earthquake etc).
Finally, the phenomenon is supernatural like magic, or curse or faith.