The 12 principles of animation established by Disney animators, including Ollie Johnston and Frank Thomas, have been represented time and time again in classic films. Though digital animation is now the standard -- it was "The Wonderful World of Disney" that first inspired current president of Pixar and Disney Animation Studios Ed Catmull to be an animator.
In the video below, the actual principles in "The Illusion of Life," by Johnston and Thomas, have been animated. "These principles came as a result of reflection about their practice and through Disney's desire to use animation to express character and personality," Vimeo user Cento Lodigiani wrote. "This movie is my personal take on those principles, applied to simple shapes."
As Fast Company points out, these 12 principles are like the laws of physics for animation. The exaggerated movements help create the illusion of realism.