Most solo founders skip formal threat modeling because it sounds like something enterprises do with whiteboards and CISSP consultants. The reality: a 90-minute structured exercise catches the issues a $15,000 external audit usually flags first.
The four-question framework
Start with what you're protecting (assets), then who'd want it (threats), then how they'd get it (attack paths), then what you've already done (mitigations). Map these to a simple 2x2: likelihood vs impact.
Warning
The most commonly missed asset: your build pipeline. A compromised CI token gives attackers access to every environment your code touches.
For most early-stage SaaS, the highest-likelihood, highest-impact path isn't SQL injection or XSS — it's a misconfigured storage bucket or an over-permissioned API key checked into version control.