How do I assess complex building systems I don't fully get?

You can assess most buildings now, but the complex systems still trip you, the ones with many moving parts that interact in ways you cannot quite hold in your head at once. That gap is not a verdict on your ability. It is just the edge of what you have mastered so far, and edges are where you grow. Complex systems overwhelm because you try to understand the whole thing at once. The way through is to break it into parts you do understand, study how each one behaves, then look at how they connect. No one holds an entire complex building in their head. They work it piece by piece and trust the method. With the next complex system, resist the urge to grasp it all immediately. Map it out: list the subsystems, understand each on its own, then trace how they affect each other. And when you hit the true edge of your knowledge, ask someone who has been there. Mastery of the hard ones is built one system at a time, not in a single flash of understanding.