We cannot know how much natural resource there is in the ground. While the cost of finding more of a resource exceeds its present value, it is not profitable to explore. Confirmation that a resource such as oil is where we think can cost as much as $100 million, even before doing the work to extract it.
As the resource’s quantity diminishes, the value increases, and it is once again worth discovering more of it. In some cases, mining the locations already known to exist but were previously not worth the investment.
No matter how much resource there is in the ground, it will never pay to discover more of it when the present value per ton is less than the cost per ton of exploration and processing.
The prediction of how much resource there is also becomes mired in politics. There is a rejection of politically inconvenient estimates until another group of scientists provide acceptable results.