There are many factors which could render GPS navigation unavailable, and only some of them are inside the airplane. Every pilot should know how to complete a flight in the face of an unexpected technology outage!
My first instructor, an amazing fellow with 20000 hours of instruction time, had me do all my training on a '63 172 with original avionics. Once I got my license we moved into a G1000 aircraft, but those steam gauges and eyeballs are my foundation.