It can't be done.
That's a dumb idea.
No one's ever tried that before.
Show me where that's been successful before.
If it's a good idea, why isn't someone else already doing it?
I don't believe you.
This world has always been – and will always be – built by people who don't listen to critics, who don't take "no" for an answer, who believe more in themselves than the voices of a thousand skeptics.
It takes a brave person to shout "yes" while everyone else is whispering "no."