I have spoken with many people who say that their teacher is an inner one, or one whom they have only met in books. So long as having this type of teacher does not occasion self-deception (we are so good at seeing only that which fits in with our ideas of ourselves and the world), that is fine. But for me, I've needed external teachers. Recently, thinking about my early awakenings (in the 1980s), I realize that if I'd had a teacher easily accessible at the time, things might have gone very differently for me.
At the time, my teacher was in Japan. My only support was his letters, which came infrequently, in part because each of mine had to be translated and then, again, his advice back to me had to be translated. Two weeks was the soonest I could expect a reply, and that was only if my letter accurately conveyed to him what had happened to me. It's hard to remember that in those days I didn't have the vocabulary for something that is so far beyond words and beyond thought. I had to talk around it -- to point but not pinpoint. And I was talking to someone from another culture. But even these were not the worst impediments.
The biggest impediment was that I myself had a whole host of misconceptions about what awakening was. I imagined I would be completely free of all problems and conflicts, that I would never have a negative thought about anyone, that I would now experience oneness with everyone all the time. It's a tall order for one little awakening -- or even one big one! And the thing is, when these expectations didn't come to pass, I discounted what really was a genuine spiritual awakening. So the return of suffering was not only because my karma didn't come to a sudden end with one awakening, but also because, although a part of me never doubted that what I experienced was what I'd been seeking for so long, alongside that sense of trueness was a nagging suspicion that I must have deceived myself since I still wasn't perfect. It has only been in recent years that I was able to go back and see in what I wrote in those days genuine realization of Truth.
So, bottom line, it seems to me that having a teacher close at hand to whom one can go immediately after an awakening, before the mind gets hold of it and starts to distort it, is important, if not critically urgent. Otherwise, the benefits of the realization that comes out of it may be lost -- not forever -- once awakening happens, it's "in the blood," so to speak -- but for a time. For me, it was a long time.