How do I handle designing complex, integrated plants that overwhelm me?

You can design most processes, and that is no small thing. The complex, integrated plants defeat you because they are a different kind of problem. Everything touches everything, and no single mind holds all of it at once. Feeling defeated there is not a sign of weakness. It is the honest scale of the work. The mistake is trying to see the whole plant in your head at one time. Nobody can. The people who handle these break them into linked pieces, solve each, then work the seams where they meet. The complexity does not shrink, but it becomes a series of things you can actually hold. Take the plant that beats you and draw only its major blocks and where they connect. Do not solve anything yet. Just map the joints. The overwhelm usually lives in trying to grasp it all, and it eases the moment you give it a shape you can point at.