Pro tip: my garage shelf fix took 11 months and two trips to Home Depot
I spent last spring trying to bolt a heavy shelf bracket into a wall that turned out to be plaster over metal lath, not drywall like the stud finder said. After three drill bits snapped and one trip to the hardware store for a masonry bit, I finally just screwed into the lath itself with self-tapping screws and it held perfect. Anyone else ever trust a stud finder over basic building sense and waste half a year on a two hour job?
Having been through a ton of old house renos, your mistake wasn't the stud finder, it was not knowing what kind of wall you had before you started drilling. Those cheap stud finders give up on plaster and lath every single time because the lath confuses the sensor and the plaster is too thick for it to read through. But honestly, trusting a $30 gadget over your own hands and eyes was the real fail here. A quick knock on the wall or a peek in an outlet box would have told you in ten seconds that you had metal lath, no fancy tool needed. Blaming the stud finder is like blaming a map when you walk into a lake, the map only knows what you punched in. So no, the lesson isn't don't trust stud finders, it's learn your house before you fight it for eleven months.