Why do we drive on the 'wrong' side?

[Larabell]

How did we start driving on this side of the road, while most of the rest of the world drives on the other?

[Ginbottle]

Right hand drive: Great Britain, Cyprus Australia, Falkands, Malta, Jamaica, Barbados, South Africa Trinidad & Tobago, Bangladesh, India, Pakistan, Indonesia, Japan.
Left hand drive Afghanistan, Cuba, Gibraltar, Spain, France, Germany, Italy, Iceland, Mongolia, USA.
Which one is 'most drive on the 'wrong' side?'
Left hand side because it leaves the jousting hand free?, but why drive on the right? Just to be different?

[Trevor]

A scabbard was worn on the man's left thigh so that he could cross-draw the sword with his right hand. He was only able to mount a horse by putting the left foot into the left stirrup and throwing the right leg over. Trying the reverse would be ungentlemanly even if he could withstand the inconvenience of the sword's handle pressing into his groin. He brought his steed to the left-hand side of the road/path for mounting even if he intended going in the opposite direction, in which case he would mount and ride around in a semicircle to his right and end up going the other way automatically keeping to the left; understand, because of the scabbard, dismounting had to be performed in reverse and again done on the left side of the road.

[psycottish]

International shipping lanes are starboard to starboard - never port to port. The port side carries a red light, starboard green. To this day all power boats have the steering wheel on the right side.