How to… run internal cables
Once, bikes had a single gear. Then they had two, one each side of the back wheel, and you stopped and flipped the wheel over to change. When derailleurs came along, they were changed first with a rod, then with cables.
And for decades cables were fine. Simple, cheap and effective, they ran along the outside of the frame, held by little cable guides. Then the devil himself took mortal form, walked upon the earth, and before he returned whence he had come he invented internal cabling.
Some frames have proper channels joining the entry and exit holes for the cable. If you’re incredibly lucky, you might just be able to stick a cable in one hole and see it come out another. Satan’s trade-off for this is that you will never be happy in any other aspect of your life. Many of us who have been less fortunate would cheerfully take the deal.
Other frames just have two holes. You can feed all the cable in the world in one and never see it appear at the other — meanwhile in a parallel dimension there’s some poor sod who keeps getting poked in the eye by bits of cable that appear out of the ether.
You could try bending the end of the cable into the shape of the Norwegian coastline, or sliding rare-earth magnets along the outside of the frame to try to drag the cable along. You might find a hospital prepared to let you use their x-ray machine. But you will never succeed.
My advice? Give up. You won’t regret it.