What has been your costliest mistake in this hobby?


For example :I recently learned a hard lesson- I accidentally ran voltage thru my $3000 MC cartridge (kiseki purple heart).  I have a TT with 5 prong connector and a phono cable with a 5 prong connector.  I accidentally swapped where they plugged into and ran electric thru the tonearm into the cartridge.  It was a stupid - not thinking- hasty mistake. When I corrected the problem the cartridge was fried.  An avalanche of four letter words followed!

So what has been your biggest and/or costliest mistake?
polkalover

I was going through a divorce back in the mid-80s and, understandably, I wasn’t thinking clearly 100% of the time.  So, I was alone at my soon-to-be former house finishing up packing my stuff one afternoon and for some reason decided I just couldn’t be bothered with the remaining 70 to 80 of my albums still there. So I asked the teenage kid next door if he wanted them and after he looked at me like WTF?, he, of course, says - Sure!

Every now and then I’ll hear a song and remember an old album I like and think - Dang, didn’t I used to have that record?

Oh well...

Got a used Furman it-ref 15i. It made the sound dull. Yuck  Plugged AMP right into wall and life was good. Wall outlet upgraded too. 
Then got a new niagara 7000 and all was well. 
Put the Furman on the “B” system and it didn’t affect sound.
Stuff fits together or it doesn’t.  
Wasted $ on poor connects and speaker wire. Didn’t know enough back then. 
That's an easy one...

The tweak in which I was directed to take a Polaroid of myself bathing in a bathtub full of Diane St. Clair butter and then afterwards to place the photo in the kitchen freezer. 

The butter alone cost over $18,000.00. 

I mean what was I thinking (should have used the smaller tub in the spare bathroom)? 

DeKay 
I bartered with a very well regarded local dealer.  Made the mistake of thinking we were friends.  Traded a very large, very expensive oriental rug without agreeing on what I was to receive in exchange - we agreed that he would have rug valued.  Took a long time - months? - but eventually we agreed on a value, $10k.  With that, he was supposed to source a Garrard 401, build a plinth, and also I was going to get a new DAC.  He never delivered on anything - I would nicely remind him, and he’d make some encouraging noises, but 3 years later I sent an annoyed note and he freaked out. Said I was being unreasonable, we didn’t have a deal, blah, blah, blah.  Eventually, he had a guy from his shop dump the rug on my driveway when I wasn’t home. Had a new stain on it too.  Obviously haven’t talked to him since.  Oh well.  Found my own 401 in U.K., shipped it directly to Woodsong Audio (Chris Harban), who restored it and created a gorgeous plinth for me, color matched to my italian tube amp (purchased from the a-hole).  Still haven’t replaced my DAC or sold the rug, but got a beautiful tt!