When someone says to you "It will never work. You will not succeed". How you react?

I opened a new business and it only one week old and I got one response from someone who said it will not work. He said I should stop doing it and look for another job. I took his react very bad. What should I do? I believe in my work and my business. People are saying very good things about it, but this person like said it in a wickedness.