Anything technical will fail on you when you least expect it and need it most. I have even had basic compasses get broken in the middle of negotiating obstacles. A planning acronym we used to use is that works with equipment as well is PACE: Primary, Alternate, Contingency and Emergency. Primary is self explanatory, but always carry supplies to keep it working (batteries for the GPS), Alternate is another way of accomplishing the mission in case the first way is not working (map and compass), Contingency is case you can't accomplish the mission the way you initially intended, but may have another way of doing it (Knowledge of major terrain features and navigate from memory, button compass in your survival kit) and Emergency is when SHTF and you are just trying to survive the experience (flare, strobe light, PLB or a good route out to safety, overdue on your plan you left with friends).