Let’s kick off by identifying all third-party systems that interact with our sensitive data. Why is this fundamental? Well, knowing what we're dealing with sets the stage for gauging potential risks and vulnerabilities. You don’t want unknown players in the game, right? Ensure you have access to system inventories and audit logs. Challenges might crop up if system boundaries aren’t well-defined, but regular audits will keep you on top. Gather your resources, maybe a network mapping tool and start your treasure hunt!