In my page about scenarios, I emphasise that you need to start with a Character who has a Challenge, has to make decisions then see the Consequences.
In this article Here’s How to Build your Next Scenario, Tom Kuhlmann suggests some reusable patterns for scenarios.
Here’s an example – deciding whether or how far to enforce a rule. The situation demands a decision.
It’s a great article and highly recommended.
How to Build your Next Scenario