These are the 3 constraints that I use before I start building anything. I'm a believer in constraints as an enabler for creativity. Constraints help us collapse the search space, and figure out innovative solutions to problems.
I've been a builder for 10 years, and I've built products that went nowhere because they were either too complex or had no identity. These are the constraints that I landed on after making those mistakes.
One page or it doesn't get built
This constraint limits complexity and ambiguity.
Write a one pager for all of your ideas. Your one pager captures your north star. It's non-negotiable, precise, ambitious, and lean. Once your one pager is written, it is applied to all different types of communication. Share it as a memo for investors, contributors, team members, friends, or family. Working collaboratively on a product, there will always be contention points and conflict, it can sometimes be difficult to know what battles to pick. If it's not in the one pager, then it's either not worth fighting over, or the one pager ought to be amended to include the thing. Not only is a one pager useful for communication, it's useful for organising your own thoughts. If you can't fill one page, don't fill the gaps with fluff, it means you're not ready to build. First research, plan, prototype, then write the one pager again. Iterate. If it requires more than one page, it's too complex, don't build it.
The core tech must be separable from the product
This constraint limits you to ideas that have real leverage and originality.
Develop a core piece of technology that supports your product and is not the product itself. The core tech is a method, skill, tool, or even product that supports what you're doing today but must survive without it. It's a type of reusable IP. Why? Separating the core tech forces you to think beyond the product that you're building. Products pivot in direction all the time, while your core tech is constant and compounding. Compounding efforts have non-linear gains over longer time horizons. Linus Torvalds developed git to improve the Linux kernel development workflow. HashiCorp has HCL (HashiCorp Configuration Language). Google has Kubernetes. But you don't need big tech resources to build core tech, it could be a library that you extract from your codebase, or even a methodology that you refine and commit to. Your core tech is your long term commitment. It is independent of your product's direction. However, it must be aligned with you or your company's long term vision. If your idea doesn't enable core tech, then it isn't high enough leverage.
One defining constraint must shape the product
This constraint limits feature creep and forces identity.
Define your own constraint that is front and centre to your product. That means the user sees and interacts with it all the time. It is obvious and it is what gives your product identity. A good constraint gives your product a feel, it permeates through all parts of the user experience. Minecraft is built entirely from blocks. IKEA is flat-pack, self-assembly furniture. The constraint that you choose limits scope by reducing your decision space, enabling you to concentrate on the problems that really make the difference. If you don't choose a constraint, or choose a bad constraint, you will build a bloated product that will try to do everything. The design of your product will "fall out" of a well-designed constraint. Like in your product, your constraint must be front and centre in your one pager.
Closing Rule
When it comes to deciding what to build, if it fails any of these constraints, then I don't build it.