At its core lies the relationship between banking and the resulting flight path, and the fact, difficult at first to accept, that neither can be felt. The inner ear, and with it its sense of balance, is neutralized by the motion of the flight. The airplane could be momentarily upside down and the passengers would not know.
Full rolls are the purest expression of flight.
They are normally flown only in fighters and other acrobatic airplanes, but if you ignore convention, you can fly them in any airplane, including a Boeing 737. Now he rode 'above' me in the bank, leaning into the aisle as if he feared toppling into my lap. He need not have worried. If he had dangled the pen from a string, it would have hung at a ninety-degree angle with respect to the tilted floor. On land or at sea it will hang toward the center of the planet.