It's difficult to steer complex systems correctly, because no one has a complete picture of the end goal at the outset. That's why waterfall fails. Writing code agentically means you have to go out of your way to think deeply about what you're building, because it won't be forced on you by the act of writing code. If your requirements are complex, they might actually be a hindrance because you're going have to learn those lessons from failed iterations instead of avoiding them preemptively.