Several great men have practiced and preached different ways of such activities. However, temporary spurts of feeling good do not lead to any permanent transformations. This is evident from the rate with which such phenomenon have arrived and vanished. One reason for the failure to accomplish any thing major through these exercises may be the fact that enough importance is not placed on the importance of completely understanding the concept of Guru. If this could be possible, then where is the necessity for Guru, for the objective of a meditation is the merger of meditator and the object meditated upon.
Human intellect responds to attributes that it can easily relate to.
Such an object makes the pursuit of the unknown easier. In fact, it becomes absolutely necessary for some, given the frivolous nature of the mind. Reference to Satan in some religions and Maya in some others probably indicate the same predicament. The necessity for a Guru is well explained in scriptures. Guru's manifold functions, and the fact that Guru is the closest to God one can experience is also well illustrated.