Happens to the best and worst of us - probably because none of us are dispassionate about our hobby and we get excited to try the new tweak, cable, position, next album, etc. and forget the logical sequences. I have made most of the same errors you describe at some point.
My worst offense so far is that I was hooking up my bare speaker cable ends in the back of amp by feel and managed to arc across positive and negative terminals (I apparently don't feel that good). When I turned my amp back on the sound came out muted, I turned the volume up (DOOH!) and all sound stopped. I opened up the amp and two of tree fuses were toast. Thank God and engineers for fuses. The silver lining is that I replaced the stock fuses with HiFi Tuning silver jobs for an overall improvement in sound. I fitted my cables with banana plugs to eliminate the chance of doing that particular stupid thing again.
