Bend your middle finger and place the centre section on a table or hard surface. You will be able to lift your thumb, index, and little finger without moving your middle finger. But it is impossible to lift your ring finger.
What is happening?
The tendons in your fingers are independent from one another apart from the ones in your middle and ring finger. These tendons are connected, so that when your middle finger is folded down you cannot move your ring finger. It feels like your ring finger is stuck!