There are many examples of great innovators accomplishing the seemingly impossible.
The latest one I came across is the story of Telstar—the world’s first communications satellite.
You should read all of the naysayers’ comments in that article, in detail.
Because that detail shows both the enormous scope and difficulty of the problem, and of how little faith the vast majority of engineers had in the feasability.
(That they overcame these problems in just two years is mind-boggling. Why can’t we build things this well or quickly anymore?)
When that many smart engineers, scientists, or businesspeople tell you it’s impossible, there is one overarching reason you should ignore them and do it anyway.
Since nobody else thinks it can be done, they’re not trying, and you will be first-to-market. It will take anyone else a while to catch-up (and when they do, it may be through espionage, so start being paranoid about the security of your documentation and communications now).
But listen carefully to their criticism, for in it you will find a nice list of the problems you must overcome.
When you succeed, please thank these people for increasing your resolve and doing a bunch of your homework for you.