During Franklin D. Roosevelt’s discussion on a new idea, one of the assistants chirped in “You can’t do that!”, to which Roosevelt responded, “I’ve done a lot of things I can’t do”.
What a great and infectious attitude to have.
There are always plenty of people around to tell you that you cannot do something. Rather than feel down about other people’s pessimism, see it as a minor challenge to overcome.
If you are lucky, often you will have close friends and family to support you. Most crucial though, is your belief in yourself.