Your single most significant purchase mistake?

Raven Audio Blackhawk. This product was over-hyped on these forums. I bought one and found it to be below average. Sold it at a significant loss. 
 

 Peachtree 125 - bright, bright, bright  

bowers and Wilkins CM10s - sterile, thin midrange. Sold it within a year. 

Forgot to add Topping D90 dac. This was supposed to be best measuring dac that was a giant killer. Hyped up on ASR. Boring, sterile, etched sound. No soul.