The Mechanics of Throwing

The second thing you need to be aware of is something that everyone has overlooked, and that is "pivot ability".

Hold a dart in your hand, sideways, pointing it to your left, if you're a "righty" and to your right, if you're a "lefty." Slowly, and repeatedly, make the arm motion as if you are going to throw the dart. Watch your thumb nail! As your hand comes forward, notice that the thumb is pivoting on the barrel's surface as the dart barrel is staying relatively horizontal.

This is imperative for consistent throwing because if your grip was too good, the dart wouldn't come off your fingers naturally due to it sticking to your skin, and if the surface was too slick, the dart would also come off your fingers in an even more uncontrollable manner.