Why do we board an aircraft from the left

Have you ever boarded a plane and wondered 'why do we board from the left'.

The reason for boarding and deplaning passengers from the left-hand side of the plane has several explanations. One explanation is based on traditional nautical customs. 

A U.S. Air Force pilot explained that airports were designed so aircraft could stop in front of the terminal to discharge passengers. This positioning helps the pilot control the wing's position relative to the terminal building and aligns the plane's door with the terminal's door. While some older forms of transport have doors on the right side of the passenger cabin, the pilot's view takes precedence.

Commercial pilot Andrew Stagg suggests that the practice originates from ships, which have a port side (left) and a starboard side (right). Passengers would embark and disembark through the port side, and airplane and jetway designers followed this convention.

For safety reasons, passenger movement is restricted to one side to prevent confusion. The right side is typically used for fueling, loading, and unloading baggage and cargo, keeping these activities separate from passenger movements.

Most modern planes board and deplane from the left-hand side while technical operations occur on the right-hand side.
Until the 1960s, before jet bridges were common, airplanes often parked close to and parallel to the terminal.

With the captain sitting on the left and responsible for taxiing and parking, this configuration allows easier control and judgment. Airplanes are fueled on the right, bags are loaded on the right, and most cleaning and catering vehicles also operate on the right-hand side.