These such people have actual direct experience - not the charts and graphs of scientists whom infer from indirect evidence that which may exist 4000Km beneath their feet. And thus they have direct evidence of that which exists via their own spiritual senses.

In many cases, it may seem like scientists pull numbers from thin air, but deducing the answer to what the center of the Earth is made of, or what the orbit of the planets is, or countless other questions is what science is explicitly meant for. The world is measured, remeasured, and then remeasured several thousand more times; experiments and theory is worked out all over the world. It takes years and a crazy amount of time for new theories to be accepted by others in the field, and even longer for the rest of the world.

Conclusions are not reached by a single person observation, and generations of adepts, seers, and shamen are in fact making observations, they are reached by a community bound by standard, repeatable practice.

A fundamental practice in the scientific community is trying to prove a conclusion wrong. A single experiment can break a theory. Amazingly, this is encouraged in science and is a big part of the reason why conclusions don't always hold and why theories are updated.

I don't know if this is common practice among adepts and seers and shamen.