I recall seeing somewhere that an airplane is a machine that wants to fly, the engine and controls just help it along. A helicopter is a machine that desperately wants to crash, the engine and controls constantly fight against this.
You are probably thinking of Harry Reasoner's quote:
"The thing is, helicopters are different from planes. An airplane by its nature wants to fly, and if not interfered with too strongly by unusual events or by a deliberately incompetent pilot, it will fly. A helicopter does not want to fly. It is maintained in the air by a variety of forces and controls working in opposition to each other, and if there is any disturbance in this delicate balance the helicopter stops flying; immediately and disastrously. There is no such thing as a gliding helicopter.
This is why being a helicopter pilot is so different from being an airplane pilot, and why in generality, airplane pilots are open, clear-eyed, buoyant extroverts and helicopter pilots are brooding introspective anticipators of trouble. They know if something bad has not happened it is about to." -Harry Reasoner
(I got the quote from
http://www.ga-vhpa.org/musings.html, and also Tim Setnicka quoted part of it in his book 'Wilderness Search and Rescue')