From Jakusho Kwong's thoughtful book on meditation No Beginning, No End, a lovely-encouraging image in Chapter 3 ("Half Moon Makes Full Halo"):
... I used to think that because only one half or one quarter of the moon was showing, there would be no full halo. But it turns out that even a twenty-five or fifty percent moon makes a one hundred percent halo. Whether it is full or not, the moon reflects that much light.
We should know that it is the same with us. When we cultivate our understanding and become aware of what we are doing, and actually see what is happening within ourselves and around us, we have that same kind of full halo. We don't have to wait until we can sit in full lotus, or until we have been sitting for ten or twenty years, as if only then something will happen. Some of us sit cross-legged, some half lotus, some full lotus, and some Burmese style or in a chair. These are only different views of the same moon. There are people who think that one form is better than the other, but it's not true. We are truly like the moon: Any amount of light makes a full halo.