[Imladris]

Well, without a guide one is lost unless they themselves know the way. If you yourself know the way, then you are guiding yourself.

What Tolkien is saying is that if you don't know the way, then you cannot "guide" yourself. If you do not know the way, then you need a guide, aka, someone who knows the way. If you don't have one, then you will wander aimlessly.