Thinking is abstract enough in itself, and unconscious or Id-type thinking is difficult to describe. I find the best way to understand it is to regard it as being similar to De Bono's Lateral Thinking. Ideas do not follow a logical sequence, but take place in jumps - the gaps are filled in later. Venus and Uranus, the other Air planets, can only cope so far with evaluating this otherness. The Moon comes and goes - literally, waxing and waning.
Feelings come and go too.
The Moon, Cancer and the Eighth House are all to do with things that come and go. The ebb and flow of life. Birth, marriage, death, probate. Beginnings and Endings, the natural flow of things. Filling and Emptying - the Tao of the 8th House.