You hit a pipe? That's my nightmare right there. I used to be the same way, thinking I could just knock and guess. Then I put a screw right into an electrical wire behind my bedroom wall. The bang and the flash scared me half to death. I bought a decent stud finder the next day and I won't even hang a picture frame without it now. Those things aren't perfect, but they're a whole lot better than causing a flood or starting a fire.