Some of y0u may have always wondered this, or why we all mount our motorcycles from the left side. Well if you have today's your lucky day! Some people have assumed that theyre on the left because when you rode bicycles the chain and drive were all on the right so they just put it on the opposite side. I've even heard that some people think its on the left because motorcycles always have their exhaust on the right (which is not the case). The reason is actually much much cooler.
The whole mounting from the left started way back when people started using horses as their main form of transportation. The earliest example of mounting a horse came from the ancient Greek general Xenophon (c.430-c.355 B.C) in his book The Art of Horsemanship which described mounting the horse from your left side. Back then you generally were carrying a sword and because most people are right handed, you would wear your sword on the left. Mounting a horse from the right with a sword on your left would almost guarantee a stabbed or hurt horse which I imagine would not be an ideal situation when you're trying to get on one of those.
Because of that reason horses have always been mounted from the left, even today when most sane people don't carry nice big broad swords when they're riding their horse to the market. Because of this tradition bicycles, and motorcycles have always been mounted on the left. Humans are creatures of habit and the motorcycle is referred to as a "steel horse" on occasion, so the tradition of mounting from the left has just carried on!