"Still, you may ask me, if its results are to be the frlund of our final spirittual estimate of a religious phenomenon, why threaten us at all with so much existential study of its conditions? Why not simply leave pathological questions out?
To this I reply in two ways: First, I say, irrepressible curiosity imperiously leads one on; and I say, secondly, that it always leads to a better understanding of a thing's significance to consider its exaggerations and perversions its equivalents and substitutes and nearest relatives elsewhere. Not that we may thereby swamp the thing in wholesale condemnation which we pass on its interrioor congeners, but rather that we ay by contrast ascertain the more precisely in what its merits consist, by learning at the same time to what particular dangers of corruption it may also be exposed.
Insane conditions have this advantage, that they isolate special factors of the mental life, and enable us to inspect them unmasked by their more usual surroundings. They play the part in mental anatomy which the scalpel and the microscope play in the anatomy of the body. To understand a thing rightly we need to see it both out of its environment and in it, and to have acquaintance with the whole range of its variations. The study of hallucinations has in this way been for psychologists the key to their comprehension of normal sensation, that of illusions has been the key to the right comprehension of perception. Morbid impulses and imperative conceptions, 'fixed ideas,' so called, have thrown a flood of light on psychology of the normal will; and obsessions and delusions have performed the same service for that of the normal faculty of belief" (The Varieties of Religious Experience, 25-6).
I am curious why James thinks it so important to study something in and outside of its environment. If something is out of its environment, it is likely not to perform as it was created. If we take a fish out of water, and place it on land, watching it flop around for a few minutes before suffocating, we will learn what a fish does when it is out of water, but why? Yes, we learn many things about the nature of the fish out of its environment—but the fish dies. So, there is a sacrifice. One thing is gained, and another is lost. What if we did this to every fish in the world, we would be out fish. And we would need to do this to every fish to truly know what every fish does when it is out of water, just so we can be sure our hypothesis is true and cannot be proved false. My point is, one, we can't observe everything in and out of its environment. Besides, as soon as the subject knows it is being observed, it will behave differently. My second point is, some things are not meant to function out of their environment: airplanes don't fly underwater.