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
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Buying brand new what I thought was “ state of the art” only to find out 1-2 years later that was “out of date” and new changes had happened HDMI for instance and now my 6k gear was worth only $1k and couldn’t be upgraded.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