Movement is the principle of design that recreates action on the canvas. The main reason this happens is because diagonal lines represent movement to us. When our eyes see something going diagonally, we think it is moving. This is why diagonal lines often lead us to what’s called the vanishing point in the art world.
There are often diagonal lines - whether clearly painted or hidden behind the paint on the canvas - on a painting or in a piece of artwork. The diagonal lines trick our eyes into thinking that something is moving, when it’s actually staying still. This is the secret to many optical illusions that seem to move in and out if you look at it properly, or unfocus your eyes.