Why do my ears pop if the cabin is pressurized?
Here is an illustration of how cabin pressure changes during a typical commercial flight:
image source: http://aerosavvy.com/aircraft-pressurization/

Note how when the pressure outside the aircraft is changing, the pressure inside the aircraft is also changing, but not as much.

During the flight shown here, you would experience about the same pressure changes that you would in an unpressurized Piper Cub that only went to 7000 feet.