Why Do Some Countries Drive On The Left?

When I was in Australia and England I dare to rent a car because it is awkward for me to drive. It is easy to take the taxi. Remember 2/3 of the world is driving on the right. Here is the reason it is mind boggle but I found this clip by accidentally. I don't like anything relating to the King and Queen so England and Australia are not my vacation destination. Beside since I grow up till now, I get used to right side of the road.