Why does my ring finger move with my pinky?

[the pianist]

When I play the piano whenever I use my pinky my ring finger copies it. And it is so hard to make my pinky move alone. And with my ring finger too. My middle finger does the same move whenever I use my ring finger. If I use my ring finger or pinky while trying to make the others stay still I can't seem to lift it as high as I can lift my middle or index finger. Is it because the nerve is connected? Is there a way to loosen them (without injury) so my pinky and ring finger could be independent? I tried spider exercises but as far as I know they are only for guitar. And when I go to piano, spider doesn't seem to help.

[brogers70]

Many people will tell you (correctly) that the third and fourth fingers share a tendon. It is the extensor tendon, the one that lifts the finger that they (partially) share. If you keep all your fingers down, and try to extend the fourth alone, it will likely not rise as high as the others can. It does not matter. The second and third fingers also have overlapping extensor tendons. However, the problem for finger independence does not come from the extensor tendons but from the brain. In ordinary life, you rarely need to operate the fingers independently, other than the thumb. For most activities, when you grasp with your hand, all the fingers work together. So you need to train your brain to operate them separately. It is definitely NOT a question of stretching or loosening tendons or even muscles, just of training your brain so that it sends signals to each finger individually, rather than as a group.

There are good exercises by Dohnanyi that will torment your brain (not your fingers) until it learns to control the fingers separately. When doing them, preferably do them with a teacher, so that you don't try to force things and hurt yourself. Basically, it helps when working on them to remember that you are working on your brain, not your fingers, so that very little force or tension is required. Go slowly and pay attention to the connection between the mental image of the correct fingers moving (or staying still) and how it feels to gently get them to do what you want. It takes time, but if you think of it as a mental game, it's sort of fun.

https://imslp.org/wiki/Essential_Finger_Exercises_(Dohn%C3%A1nyi%2C_Ern%C5%91)