Actually, it is a matter of common sense, but not everybody is born with it.
So, you have a soft, piece of material that needs to be attached to a rigid surface. There is a hard skeleton type piece that goes inside it to help it maintain it's shape so that it can be attached. Is there anything there that will keep this extrememly flexible object is place, and in shape without that skeletal piece? Nope, I don't see anything, looks like a new part is going to be needed. "Master of the obvious", indeed.