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
selling my trl gt 400s, gtp preamp, and soundlab a1s. still chasing that lost Magic! rip P.W.
My costliest mistake was to buy nearly one thousand vinyl LP's over the decades that had only one song on the album that I liked.

The 'one' song per album I liked cumulatively proved very expensive.
Buying brand new what I thought was “ state of the art” only to find out 1-2 years later that was “out of date” and new changes had happened HDMI for instance and now my 6k gear was worth only $1k and couldn’t be upgraded. OUCH
I purchased Bob Carver M350 Black Raven amps and I thought they were great! I still do!
But, I thought that if the amps were so great then with his speakers together they must be a great combo. Wrong big time! The speakers required so much power that the amps meters were pegged, fuses blew, and they had a terrible sound. 8000hz and up was a disaster. Traded them in quickly for a big loss. 

ozzy