Everyone has dreams. Most never realize them; not because they're impossible but because they're unwilling to put in the work. The wildest dreams do not necessarily take more work than the simplest, but they are prone to additional ridicule from naysayers. That's OK, because you can prove everyone wrong — if you're willing to put in the work.
Working toward your dreams involves more than just saying “I can do it.” It means doing it, whatever “it” is. Don't be afraid to go out on a limb, and don't lose confidence simply because it takes time. Sources say it takes three years for a small business to be profitable; 10 to become a millionaire. And those are optimistic statistics.
Of course, businesses can be sold for tens of millions within months of starting up, but not without hard work.
Here's your challenge: Realize that when people say your dreams are impossible, they're not saying that they can't be done. They're saying that YOU CAN'T DO IT. It's an attack on your person, your confidence, your abilities, your resources, your gumption, determination, dedication, intelligence ... everything that is YOU. Once you've realized this, channel your disappointment/anger/sadness with reality into constructive energy you can use to enact your plans and achieve your goals.
You can work easy your whole life, or you can work hard now and live easy later. The choice is yours. Can YOU do it?