You will probably agree with me that sitting on a one-legged chair is somewhat unstable. A two-legged chair also provides only little stability. A tripod is better, and a chair with four or more legs allows for fairly secure seating. How many legs does the chair you're sitting on have? At first glance, it seems like nonsense to try sitting on a one-legged or two-legged chair, yet this is exactly what many people do. More here.