Unable to place new clip into project timeline with Final Cut Pro

I'm trying to place a clip into the middle of an existing project. Typically when I try to do this, the two clips I'm trying to place the new one in-between slide over to either side and allow for the new footage to move in-between. However, for whatever reason with the current clip I'm using, the existing clips do not move to either side, and the new clip instead just plays over whatever was there originally.

[Re-Titled by Moderator]