Your single most significant purchase mistake?

2 examples come to mind...a trapezoidal shaped Kenwood receiver with a space age LED pad remote that had a shape to match.  Oh and also the Kenwood that came with the blue smooth membrane remote, Kenwood tried hard after the classic silver-face days to bring innovative space age looking designs.  The products just weren't ready for prime time.

And even worse, and some years earlier---a "home theater" set of Pinnacle speakers bought at hi-fi-fo-fum in Lawton, OK.  The subwoofer even was passive.  Only speakers I ever had that had a zero excitement to its sound signature.

Oh sorry it was supposed to be singular---I don't like abiding by rules. If I were pressed---the Pinnacles.

Weaver likes 6 figure everything, has a head twitch, and a martini issue. I try very hard to avoid his over the top bombastic pomposity. He uses the same 100 adjectives over and over...I tired of him after the first 10 episodes.  Perhaps that is the time waster I regret most..lol.

Most of my adult life I wanted McIntosh. After an accident and reward from it money I bought McIntosh. Sales experience horrible, no questions of what I listened to or solid state versus tube. So I can tell you that I have found much better sound at a fraction of the cost. I could have been sold better, educated better and maybe had spent more but because of all the above my Mac experience was a true disappointment 

My biggest mistake was not anticipating how much fun this hobby would be and so started out not spending what I could have and therefore continually upgrading. For example, I went from a Rega P6, then an 8, then a 10, and then scrapping the brand altogether and bought a Bergmann table.  Same with the phonostage- went through 3 before getting what I ultimately have kept.  Same with my preamp/amp - started with an integrated and went to separates pretty quickly after that.  Each time losing some money all the way and let me tel you it adds up!!!!

Biggest mistake was dealing with Mike Powell   Bought a pair of AGD Tempo GAN amps and just didn’t work out in my system. Sent them back within 3 weeks of the 30 day trial and he said he spent my money. He pieced me back the 9k over a 10 week period while calling me names, and dogging my system. 
The dude is just the worse dealer by far I have ever dealt with….stay away