My attempt to build a floating shelf ended with a hole in the wall

I saw a video online about making a simple floating shelf with just a 2x4 and some brackets. I measured everything twice, or so I thought. After I drilled the pilot holes and went to mount the bracket, the whole thing just ripped out of the drywall. Turns out I missed the stud by about an inch and a half. Now there's a fist-sized hole where my shelf was supposed to go, and my cat keeps trying to climb into it. Has anyone else had a stud finder lie to them like this?