Why is it easier to fly a kite with a tail?

A kite flies better without wobbling, spinning or diving if it can keep itself inclined at a specific angle against the blowing wind. This creates a difference in the air-pressure around the kite in such a way that the kite is lifted up. The tail helps a kite in keeping its angle of inclination stable by pulling down its lower tip. Without the tail, wind blowing against the kite and the lift-force generated in turn would send a conventional kite into a tail-spin. Box-kites, however, do not need a tail to stabilize as they do not need to maintain a constant facing angle against the wind to generate the lift. The air swirling through and about a box-kite creates all the pressure differences required to lift up.