A thing is not esoteric because it is secret or kept hidden. It is esoteric because its existence is in some sense unmanifest, private, and by its very nature not available for examination from the outside: it is only available to participation, not, ultimately, merely to examination. In other words, the realm of the esoteric is, before anything else, the realm of consciousness, of experience.
Earl King, Jr., Having and Keeping Secrets: Some Words About Silence and The Hermetic Art of Secrecy