How to Narrow Down Your ICP and Pick the Right Use Cases

How did you narrow down your ICP and figure out which use cases to focus on? There's two ways to do it. One is if I had just started with this problem anew, because I had only had a technical innovation in mind, then I would have to do some sort of breadth first search. Some of it was frankly random. For example, should we do more SaaS data residency or more PCI like stuff for FinTech companies,. Was a toss up and I picked based on my personal preference or where I had the most network to begin with.