They Get Bigger!
Tension in a story should go up! What makes it go up? Obstacles and challenges getting bigger. The land gets more hostile. The food runs out. The enemies get stronger. The resources to tackle each diminish. Strength fades. The odds of achieving the objective become insurmountable. Tension rises!
They Reveal Character (called tests in some formulations)
How your protagonist deals with a crisis, or obstacle, tells us who they are. There are ten people standing around in business suits: how do we know the character of these people? By showing how they react when the bomb goes off. Do they flee for their own safety? Do they immediatel think of helping others? (remember a hero is someone who sacrifices themself (yep) for others) Do they worry that their clothes will be ruined? Do they immediate start the search for justice and revenge? Or do they crumple up and die?
They are Related to the Main Story
Obstacles that do not contribute to the trajectory of the main story line in some way often feel contrived and inconsequential. The pace may feel slower, and the audience’s interest may dwindle if the obstacle your protagonist is facing does not arise out of their desperate need to achieve their objective. Let’s say someone needs to take their child to the hospital because the child is suffering an asthma attack. If on the way to the hospital the protagonist drives past their old high school, and stops the car to discuss some unresolved high school drama, this is going to feel weird. In Final Fantasy 7 Remake (yep) there’s a whole passage where the protagonists have to pass through a haunted warehouse and its just has nothing to do with the plot and is stupid (deep breaths).
They Require the Protagonist to Learn Something New to Conquer Them
Great obstacles require the protagonist to learn a new skill in order to conquer them. The value of friendship for instance, or the ability to conquer fear, or perhaps even something like using a grappling hook … obstacles build your protagonist into a better version of themself (I’m going with it).
They are Inevitable yet Unexpected
Things that emerge in your story, like obstacles, should be inevitable yet unexpected. What in the world does that mean? Well, things should be unexpected because then they are more thrilling! That seems straightforward. What about inevitable? Take Lord of the Rings for example: the perfect example is Gollum jumping on Frodo as he attempts to throw the ring into the Crack of Doom. Nobody sees that one coming, and yet of course! It’s exactly what Gollum would do. It’s why he’s been following them all along, and what other choice does Gollum have in that moment? Unexpected yet inevitable! Enjoy!