Guest.IS wrote:
I think it's a very deeply rooted and ancient phenomenon, to think in threes. Georges Dumézil theorised about what he believed to be the 'tripartite' organisation of Indo-European cultures. Obviously in so-called 'Celtic' culture it's very prominent - not just in the Welsh triads but equivalent early Irish texts, the symbol of the triskelion and the notion of the 'triple goddess' a deity with three contrasting yet complementary aspects. Also the Greek Fates, Norse Norns, etc. Countless examples of this phenomenon across time and cultures.

Brahma, Shiva, and Vishnu in Hinduism. Gods seem to go from one to three very naturally, without stopping at two. :-)

The Hebrew Bible is divided into Torah, Prophets, and Writings.

Burgundy was the "Middle Kingdom" because it was the portion of Charlemagne's empire between France and the (rump of the) Holy Roman Empire.

In the Middle Ages, armies were almost always organized into three wings (divisions, battles, whatever), whether left/center/right or van/main body/rearguard. The King commanded the center, and his two senior officers (dukes or whatever) the two outside wings. I don't think that's some magic rule of three, though; it's more a tactical help: you can devote the larger portion of the army (i.e. two divisions) to one task (attacking or whatever) and the smaller portion (one wing) to holding its position. The number of medieval battles that followed that pattern was very high.

If you're determined to find threes, you probably will. Although, chances are, if you're determined to find twos, you'll find those, too. :-)