I've heard the phrase navel gazing exactly a million and one times, without ever suspecting that it had once been more than a figure of speech. I thought that it merely involved contemplating yourself, and a particularly uninteresting part of yourself at that.
The term is only recorded in English from 1854 when Harper's Magazine had the line:
Therefore‥every man who has contemplated his own navel until he is solemnly convinced that he has seen to the bottom of it‥is cocksure that he can help the world.
Thus my joy and jubilation when I realised that there were once real navel gazers who took the matter seriously. The Hesychast monks of the Middle Ages would sit on Mount Athos contemplating their belly buttons in order to achieve spiritual enlightenment. Here are Abbot Symeon's instructions on the matter of meditation:
Sitting alone in private, note and do what I say. Close the doors and raise thy spirit from vain and temporal things. Then rest thy beard on the breast and direct the gaze with all thy soul on the middle of the body at the navel.
The Hesychasts therefore became known as the Omphalopsychites, which means, approximately, navel-spiritualists. They were also called by the Italians the Umbilicani.
If a belly button is actually a pre-requisite of spiritual purity, it is no wonder, if you think about it, that Adam and Eve fell.
This picture contains two mistakes.