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
Adding damping material tweak to my 15" woofers... when removing one of the woofers from the enclosure I dropped it resulting in the magnet moving and locking the voice coil... Slick move trying to get that final 0.001% improvement that killed a woofer that is no longer manufactured.  So after 6 months trying 3 pairs of woofers w/ similar thiel parameters I finally landed on a solution with a minor crossover change.  Note there is no damping material on the new woofers and I'm perfectly fine with that.  Ugg.
I bought a pair of Carver Silver 7 tube monoblock amps at an estate sale. Paid $250 for both.

Ive been offered $8,000. Each.

I still have them. But my wife reminds that I can sell them, every time we need quick cash.

i should never have let her see the text I got from the seller; the 23 year old kid who sold them to me at his grandfather’s estate sale. He still texts 3-4 times a year, asking if he can buy them back.

At the time I bought them, I was the only looker. I told him they were “organ amps” from an old Hammond electronic organ... not worth much.

So the kid is mad at me, my wife is mad at me.

I have a big smile on my face, every evening at 6:30 pm....
What has been your costliest mistake in this hobby?


Maintaining this hobby......
Tons of costly experimentations, my latest decision is one for the ages, I decide to install a secondary system in my basement to let my wife sleep better while I could listen to live music level downstairs thinking that I could be happy with a basic system...read limited budget...God how naive... I’ve spent 2/3 of my initial budget on room treatment alone and I’m wondering where it will end.
My wife still complaints that the music is too loud as well...
costliest mistake in this hobby?  it's "Starting"...according to my bank account