According to the theory of persistence of vision, the perceptual processes of the brain or the retina of the human eye retains an image for a brief moment. Persistence of vision is said to account for the illusion of motion which results when a series of film images are displayed in quick succession, rather than the perception of the individual frames in the series. In drawn animation, moving characters are often shot "on twos", that is to say, one drawing is shown for every two frames of film (which usually runs at 24 frames per second), meaning there are only 12 drawings per second.

Even though the image update rate is low, the fluidity is satisfactory for most subjects. However, when a character is required to perform a quick movement, it is usually necessary to revert to animating "on ones", as "twos" are too slow to convey the motion adequately. A blend of the two techniques keeps the eye fooled without unnecessary production cost.

Traditionally-animated productions, just like other forms of animation, usually begin life as a storyboard, which is a script of sorts written with images as well as words, similar to a giant comic strip. The images allow the animation team to plan the flow of the plot and the composition of the imagery. The storyboard artists will have regular meetings with the director, and may have to redraw or "re-board" a sequence many times before it meets final approval.