What has been your costliest mistake in this hobby?

@stereo5  I've read of your problems with the VR33s on AudioCircle.  It could be any number of problems but they didn't work in your room.   Nearly all of the owners wrote that it could have been your room/floor/acoustics, cabling, equipment, etc.  Something didn't jive for you.  I own speakers some people hate.  The reason is they are trying to play my big speakers in small rooms-it doesn't work.   

Agree with Kenny, starting hobby....  actually not too many mistakes except for  buying a used VTL..... that was a costly mistake.....   some "lifetime transferable warranty" that proved to be.

My cat enjoyed the comforts of the heat radiating from my Mark Levinson amp.  Unfortunately he apparently couldn’t control his bladder and the result fried the circuit board. I got about $100 for the salvage parts.

Asking my wife. 

Need a further explanation? I paid for it alright.

I have, on occasion, sent prime examples (VERY low hours) of tubes from my NOS, backup stash, to AudiogoN members who’ve asked about, "the best" of the 6SN7 and/or 6DJ8/6922 types, to taste for themselves.       A little over 2 1/2 months ago; I sent a pair of Amperex Navy 6922 (early Sixties/large halo getter/maybe 10 hrs) and a pair of early Forties Ken-Rads (bottom gettered/staggered plates/copper rods/less than 10 hrs) for a member to try in their Cary SLI-80 F1, based on what they described as presentation preferences.       They loved the presentation so much; they asked if they were for sale and- did I have anything else, that they could audition.        Glad I didn’t, because: it’s been at least a month of attempted communication, without response.       When purchased (some 20 yrs ago), I paid around half of what they’re worth now (around $500, today, combined).       Glad I’m not as bankrupt (financially or morally), but- that still stings.       No one to blame, but- myself (of course)!