What's the reasoning for safety wire on aircraft, and the reasoning behind the way it's routed?
Safety wire (positive wire locking) is done in areas where there is a possibility of the bolt getting loose due to vibration (also in other critical areas); this is done in a way such that the loosening of the bolt is counteracted by the tension in the wire i.e. in case the bolts loosen, the locking wire becomes taut and prevents further movement of the bolt.



safety wire examples; image from www.stangtv.com

There are different ways of doing wire locking for locking depending on the number of fasteners involved, but the basics are the same.



Safety wires; image from FAA AC 43.13-1B - Acceptable Methods, Techniques, and Practices - Aircraft Inspection and Repair