I use GPS for hiking, backpacking, geocaching and sometimes driving. I have never become lost while using a GPS. GPS does not have an "off" day and decide to give you a random, incorrect destination. I have had the GPS suggest routes that are not the fastest or easiest to get to a certain location. It works on the very simple concept of measuring distance from satellites and determining your location.
The problems that can come up with a GPS are incorrect information entered and out of date software. First off, if you enter your destination incorrectly it will obviously not take you to where you were wanting to go. Also, if the mapping software is out of date or something was entered incorrectly, it may lead you in a direction that takes longer, or leads to a dead end.
Don't turn your brain off when you turn the GPS on. As it gives you directions, check them with what you know about the area. Pay attention to signs along the roadway, are they consistent with what the GPS is telling you? The GPS is a great tool for navigation, but it shouldn't be your only option.