The obstacle is whatever is MOST in the way.
The term “obstacle” has many near-synonyms, e.g., in entertainment “antagonist,” or in business the “pain point,” “what keeps X awake at night,” or “the real challenge.”
Like the goal, the obstacle will have external and internal facets which mirror each other. The external facet will be something in the real world, e.g. old age, the Nazis, Mary Jane Watson. The internal facet will be emotional, e.g. fear of dying with regret, lack of faith, adolescent dreams.
This is very important: The obstacle should BE or SEEM greater, larger, more powerful, and more insurmountable. If you’ll allow me to math this up a little bit, the absolute value of the obstacle must be greater than the absolute value of the goal or else there isn’t a need for transformation, suspense, or surprise – there’s just someone getting what they want.
Again, like the goal, the obstacle is something you need to feel in your gut. You empathize with the hero and what they want, and when you consider the obstacle to that… you should feel scared, upset, even overwhelmed… like there’s no way you’re going to get what you want.
Also important to keep in mind is that the obstacle and the goal will fit together in some way (following the principle of equivalency) because both will be inherent to the hero or decision-maker.
An equivalent obstacle isn’t always a “block,” sometimes it’s an alternate goal. For example, in a classic rom-com (romantic comedy) structure, the girl might have a particular guy as her goal. The obstacle could be that the guy is still in love with HIS ex. That’s a block. Or, the obstacle could be that she’s still in love with HER ex. That’s an alternate goal. However, in both cases, only one thing can be the goal, the other is the obstacle (following the principle of singularity).
You’ve got to figure out which is which because it will make a substantial difference in how to tell the story. Strategically, the obstacle will need to be positioned as a threat, overwhelming and urgent. Tactically, you might use different language and color motifs, e.g., the way The Sixth Sense uses red to indicate the supernatural and spirit world, which represents the obstacle (spoiler alert… the hero is dead).
In a business story, the obstacle can difficult to determine because there are SO MANY obstacles. Not enough time, not enough budget, insufficient human resources, external competition, internal politics, a recent setback, market volatility, shifting geopolitical landscapes, tradeoffs between different products, or competing values such as growth and efficiency.
Plus, obstacles in a business story will change over time because as key problems get solved, other problems surface to the top of the stack.
But remember… there can only be ONE.