I predicted the original wii was going to be a big flop despite being a huge fan of their earlier consoles. I couldn't see why people would pay serious money for a gamecube with a new controller.
In fact from memory my predictions for various consoles were;
PS2: Successful (despite not being a fan of it)
Original Xbox: Successful
Xbox 360: Successful
wii u: successful
xbox one: unsuccessful
In hindsight I think my views are skewed slightly towards favouring powerful hardware as likely to be successful.