Imagep,
We are nowhere near full production as the sum of individual output in our nation. Today, you could offer me X, and if I sufficiently wanted it (And there are things I want that much), I would work more than I would have otherwise worked before your intervention. Before your marketing. That can be extended quite far out there until we reach a point where any additional effort on my part is not worth the outcome (could literally work to death!).
If you add this up in our entire population, the potential output, the already existing demand, is staggering. And it's not just hours in a day. Everyone is likely at job that they do not use their full potential even in the hours they already work. If someone finds a way to utilize that extra potential output even within the current work day, again, it's hugely valuable (globalization is a gigantic example of this playing out in real time today)
All of this adds up to the undeniable fact that within our current economy, there is a significant amount of productive wealth that is not currently tapped. Keep going though. There are people with unproductive investments right now, if you were able to sell them on a more productive idea, and you delivered, that money...we're not even talking about human potential at this point (it ends up as human potential but it starts as money), again you through a behavior choice, created value in the marketplace that otherwise would not have been there. Even if you denied all of this, you can still imagine that there are tools and technology laying around decaying right now, that if you utilized them, you could create value. If that value enhanced by those tools (pathA), exceeded your alternative behaviors (if you chose not to use those tools, call that pathB), then you created value yes?
Surely you see how we are nowhere near any theoretical maximum capacity. For practical purposes on the day to day, it's INFINITE. In reality, of course it's not infinite, but a single individual could never in their lifetime through their individual actions create a situation where the world was at max capacity. So for practical purposes, infinite. Infinite is a bit misleading though, because it gets progressively harder as we get more output. But we're nowhere near it being too difficult to make huge gains, so yeah.