There is really no reason for this but mostly it is because the designers don't it that way.
Triplets!
Monocot is differnet from dicot because of many reasons. One of the reasons is that monocots seeds have one part, while dicot seeds have two parts. Also monocot leaves have parallel veins, and dicot have net-veined leaves. Monocot flowers come in parts of threes, and dicot flowers come in parts of fours and fives. Monocot stems have scattered vascular bundles, and dicot bundles come in a ring. The roots of monocot are fibrous, and the ones of dicot are traproots. Those are some of the differences of Monocots and Dicots
That they come in threes.
The plural is written 3s or threes when referring to the number itself, or sets or groups of three. - e.g. Seven threes are twenty-one. There are four 3s in his license plate number. We divided the group into threes for the scavenger hunt.
france.
sneezing,coughing,touching
Ailien Balls.
The fingers on your hand!
Five bar gate Quintuplets
It means that a 4 piston engine is smoothly running because it's 'firing on all fours'
Midnight Sun. But it might not come out.
Clover leaves, deaths, accidents...