Unpacked road bike. Assembly is simple enough, except that the rear derailleur cable housing is not in its groove (I'm sure there is a specific term).
Here is a picture.
No matter how much I tug (manually), the lower part in the picture—whatever it's called, housing endpoint?—will not fit in its seat, or "groove".
The brakes need no adjustments out of the box, and so I'm assuming the derailleurs are likewise already tuned and I don't need to disassemble, say, the screw holding the end of the cable near the cogset.
What's the trick?