* Genetics: Just like humans have dominant and recessive genes for hair color, horses have genes that influence mane growth direction. Some horses are genetically predisposed to have a mane that falls to the left, while others are predisposed to have a mane that falls to the right.
* Dominant Side: Horses, like humans, often have a dominant side. They may prefer to use one leg over the other, turn their head more to one side, etc. This dominant side can influence the way their mane grows.
* Environmental Factors: While less significant, factors like wind direction, the way the horse is groomed, and how the mane is braided can all influence which way it falls.
* Habit: Over time, horses often develop a habit of having their mane fall to one side. This is likely due to a combination of the factors above.
It's important to note that the direction of a horse's mane is not always perfectly symmetrical. Some horses may have a mane that falls more to one side than the other, while others may have a mane that falls more evenly on both sides.