A spiritual teacher introduces you to reality. And believe me, despite protestations to the contrary from many an eager student, this is the last thing in the world anyone in their right mind really wants. This is why the teacher must first disguise his intentions and second reveal only the faintest glimmers. So faint or fleeting that the student may not appear to notice. Then it's just a matter of time. Practice helps of course but it's a moot point as to whether it's essential.