Well while we may be in the minority worldwide (see URL <http://users.pandora.be/worldstandards/driving%20on%20the%20left.htm#leftdriving
That's a very wrong website.
About a quarter of the world drives on the left, and the countries that
do are mostly old British colonies. This strange quirk perplexes the rest
of the world; but there is a perfectly good reason.
[Edit: I was wrong about China, seems they drive on the right. I estimate about 1/3 drive on the left.]
Wrong #1. Most of asia, including China, India, Indonesia, Japan, Thailand, and Malaysia (about 50% of the world's population) drive on the left.
Since he was sitting on the left, he naturally wanted everybody to pass
on the left so he could look down and make sure he kept clear of the oncoming
wagons wheels. Therefore he kept to the right side of the road.
Wrong #2. The driver passing is the one who knows that a pass is about to take place and has the greater responsibility to ensure the pass is safe.
A recent excavation of an old Roman quarry in England shows that driving on the left has been the norm for almost 2,000 years at least. The ramp into the quarry was wide enough to allow two carts, so one would ascend while another was going down. The shallower ruts of the descending empty cart are on the left.