Readers of Carl Jung oftentimes would be amazed by his spiritual guru Philemon who gave Jung lots of insights in his inner journey to the Unconscious. Jung wrote in his Memories, Dreams, Reflections, "He (Philemon) was a mysterious figure to me. At times he seemed to me quite real, as if he were a living personality. I went walking up and down the garden with him, and to me he was what the Indians call a guru". Apparently Philemon didn't physically walk with Jung but appeared to him in his vivid dreams and/or during meditation. Jung later related that one of his esteemed Indian friend also had a spiritual guru by the name of Shankaracharya, and such spiritual leaders were not that uncommon for Indians (needless to say, I would believe, ought be related to inner pursuits rather than scientific investigations).
The case of spiritual gurus was also quite common in Taoist literature. For example, Zen master Liu Huang Yang (柳華陽) learned his stuff from his spiritual guru Taoist Immortal Wu Chongxu (伍沖虛真人)(for details chick here). In addition, Grandmasters of both the East sect (東派) and West sect (西派) claimed to have learned their stuff from the same spiritual guru, great Grandmaster Lu DongBin (呂洞賓).
And according to biographies of these people, the psychic experience of having a "separate personality" who taught them stuffs was so strong that they could only believe that these spirits came to teach them and gave them insights, as if giving them an object, rather than they formulate the insights themselves and became a more learned person, like the experience of learning other things by the ego (e.g. learning mathematics) in daily lives.
This reminds me of a statement of wisdom in Chinese posted on the door of my psychology professor the late Rev Erik Kvan of the University of Hong Kong: 江山易改，本性難移(it is easier to overthrow a government than to change a person's inborn personality).
The ultimate objective of inner practice is for an overhaul of one's personality. In Taoist's lingo, it is to become an Immortal, in Buddhist's lingo, it is to become a Buddha. It is little wonder that our ego can't accept this change easily, and the psychic experience of these sages showed, it seemed to have to be imposed from outside, a transposition of new concepts into one's ego, through, as perceived by the ego, a guru with an independent mind, existence and superior wisdom (the last is to ensure that the ego could and would accept a change for the better). Needless to say, the names of the gurus differed from one person to another, as shown above.