Can't connecte anything to a configurable joint

Hello. I'm new to Unity, and ran into a problem that I couldn't solve while going through some basic stuff.

The problem was simple. Whenever I'm trying to connect bodies using configurable joints, they won't be connected, just fall apart as if they are separated objects. Even when I don't assign a connected body so that the joint would get fixed in the air, it won't get fixed, and the body just free falls. The other joints are working normally, but only the configurable joint has this problem. From tutorials, create a new project -> create a new cube -> attach a rigidbody -> attach a configurable joint -> hit run should make a cube hang in the air, but it make the cube free fall. Is there something very basic I am missing?