In light of the new consoles releasing, I thought I would propose a funny topic about the dumbest/funniest reasons you have heard someone say for why a console will not succeed. If you choose to participate in this thread please dont take it to seriously. 

Back when the Switch was first revealed, I remember somone(Colin Moriarty I believe) say that one of the factors for the switch flopping is that no one will be able to look up "Switch" on google and see a nintendo Switch, only a light switch. This is so funny to me, especially because now if you look up switch you actually see a nintendo switch. I think about this alot. 

Console is too weak

*Looks at all the times that weak consoles succeeded*

"It doesnt have Zelda in its library".

The console has no gaemz!

Or

It is an indie machine!

Or

LaSt GeN pOrTs!!!!!

Basically anything that tries to belittle a library to tip the scales in imaginary list wars. We saw it with both PS4 and Switch most recently. In both cases, much crow has been served.

Captain Yuri beat me to it, but yeah, "underpowered" is always hilarious, given that most gens weren't won by the strongest hardware and systems a gen behind in power have trounced their more powerful rivals.

Not quite the answer you are looking for a fake reason why someone thought something would not succeed but I can give a real reason NES almost didn't. Teddy Ruxpin.  For those not aware Teddy Ruxpin in the mid-80s was the most popular toy in the US. You put tapes in his back and his mouth would move and talk from the tape. It was kinda neat. Well in that time period SEARS was the largest American retailer. They refused to sell NES systems. The video game crash made them feel there is no use in selling a video game console. Teddy Ruxpin threatened to pull their product if SEARS did not sell the NES.

EVERY 80s kid looked forward to the SEARS catalog every year to point out to their parents what they wanted Santa to bring them.

As for silly comments. I do remember people online calling DS, the Virtual Boy 2 as the concept of 2 screens threw people off before it was shown off at E3 2004.

If Trump ever makes a positive comment about your new console?

To me the really dumb ones are the ones that get repeated over and over even decades later:

"Consoles are over, because there are far more PC (or mobile) users."
"It's competing against Sony."
"My console has better graphics.  Here look at this side by side comparison."
"Look how badly your console's maker did with their last console."
"It can't possibly succeed, because it doesn't have _____ game."
"It doesn't have Virtual Reality, which is the future."

..because they're in permanent decline except for when they get lucky/strike gold/hit the jackpot/fluke it.
..because smartphones

Because of deez nuts. Woman makes up a large portion of the video game population worldwide, but they will skip mobile and next gen to flock to deez nuts