Weather it's car repairs, or home repairs, always check the simplest things first

I have a Modine gas fired unit heater in my garage. Stopped functioning a few weeks ago, so I start replacing parts (things that have gone wrong with it in the past), and nothing is fixed.
Finally figured out that there was no 120V getting to the unit.
The heater is on a dedicated circuit in the garage, except for one outlet on the outside of the garage. Well, it's a GFI outlet of course, and it was tripped. When the gfi trips, everything downstream from that outlet also looses power. Pushed the reset button, turned the switch for the heater back on, and bang, fired right up.
Don't know if its old age or what, but when something breaks I always assume the worst instead of checking the basics first.