To work on a passion project you need a problem you’re solving. That is your “why.” Then you need a “what.” That’s the thing you’re creating – a club, a website, an event, a product etc..
Those two steps are relatively easy. The hard part is the “how.” It’s the “how” that connects what you’re doing with why you’re doing it.
If you set out to improve the way schools handle mental health by starting a program at your school, how you go about doing that will dictate whether or not you are successful. It’s entirely possible to start that program and have the outcome not contribute to solving the problem.
The “how” is the nuance. The “how” is the systems thinking, the design thinking, the prototyping, the iteration. The “how” is the hard part.