When it gets crushed by the passing bolts of magnets which consume the entire tube diameter because they are propelled by air and need to fill the entire tube in order to work.
If you want to run fibre along, and it's a good idea while you're digging away, do it in a parallel but separate tube.
If you want to run fibre along, and it's a good idea while you're digging away, do it in a parallel but separate tube.