What caused inboard front disc brake pad to score the rotor?

I'm having a hard time visualizing how the squeak shim made it all the way to the rotor. Did you put the pad in backwards? :poke:Photos please.

OK, guys, and let me thank you kindly for your helpful replies.

The shim between the pad and brake piston came loose, its attaching tabs got all bent up, and it rotated until the front edge of the shim hit the rim and started rubbing on it. Here's a picture. I then discovered that the inboard side of the rotor was totally scored up.

So is it important to glue the shim securely to the back of the pad with Brake Quiet glue? If the shim comes loose while I'm installing the pad, do I need to re-glue it?

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