While we can hit harder limits with some resources, like Helium, I believe most resources are far more fungible and/or replaceable. That's in part why peak oil announcements seem to be habitually premature. Reserves are at a specific price or price range, so if those go up reserves tend to go up too, and the same applies to other resources.

To further complicate things, we can replace oil in different ways depending on cost and alternatives, which also depend on time. Toss in a wide variety of different priorities, and it becomes apparent why many predictions we've made tend to be inaccurate.