There is an English expression that goes "to be on the cusp of something...". I always wondered what a cusp was. As it happened, a cusp is a bit a singular shape or object (check out a definition in the free online dictionary), it looks like this:
Where the cusp is the pointy inside of this trefoil. The same shape in this nice picture too (GNU Free Documentation License., shot by Paul Venter):
The etymology of this word identifies a point or pointed end, in an astrological sense. There is then in my opinion lost of drama going on at being on the cusp: we stand on a pointy/sharp end, when maybe only seconds before we were comfortably and happily minding our own business in a well-know environment. Our objectivity on the world suddenly shifted, an existentialist question mark burns the mind, a road sign showing "Stop"/"Priority"/green/red, a mute interrogation as the brain lacked the experiential vocabulary.
I found I was several times on the cusp of a revelation about life or existence, and nothing was more frustrating than being 'snapped' back in the mundane reality. If the trefoil above was akin a key hole, I would feel like a frustrated voyeur.
How about your 'cusp' moments? Did you have any? Any realizations on the other side?
Interestingly, the French translation for "cusp" is "etre a l'oree de..." (to be at the border of something, usually the divide between a forest and a plain). The idea of singularity in my opinion is absent from the French expression and it is replaced by a more progressive titillation of the senses and mind: one would walk in the forest and get to its limit as the vegetation slowly changes to get to the plain, or could be possibly more brutal with a sudden divide (possibly artificial, man-made barrier or deforestation...); the idea of surprise is replaced more by path or quest.
To finish, in "to be at the brink of", the word "brink" originates from Scandinavian brekka, a slope or grass lands, similar to "oree" in a sense.