GPS is a navaid, nothing else but is a very good navaid. Like all navaids it has to be checked before you rely on it. That's why you do a frequency and ID check on a VOR or ILS. A simple check of it knowing where it is and which direction it is going to send you is always required using a seperate aid or the simple eyeball.
There are people who will happily follow a GPS telling them how to get to a westerly destination whilst they are shading their eyes from the morning sun.