I sliced open my hand and cut one of the tendons. The doctor wants to operate and repair it. Won’t the tendon heal by itself?

The tendon is like a rope on a pulley. In order for tendons to move the fingers, they must be able to move or glide easily inside the lining that covers them. Once a tendon has been cut it can’t repair itself enough to put pressure on the pulley system and move the finger. It will fill in with scar tissue, and you will lose finger motion. Early repair and return to movement is advised.