One reason is the negative cynical attitude of other people.  These people are not enemies; they are friends, even family members.  If our friends are negative towards our dreams or aspirations - our friends can kill us.

A man gets excited about the possibility of a new job or a new idea.  He sees the opportunity to make money, do more meaningful work, rise to a personal challenge; revving for this stimulating new prospect. But then he tells his neighbor about it over the back fence once evening, he gets a smirk, a laugh that says, "You can't do that", a foot-long list of all the problems and obstacles and fifty reasons why he will never make it and is better off to stay where he is.

His enthusiasm disintegrates.  He loses all his fire and self-confidence and begins to think of all the reasons why he can't make it, instead of all the reasons that he can.

Friends can do more damage than a dozen enemies.  Remember, the easiest thing to find on earth is someone to tell you all the things you cannot be.  Don't listen to them.

It is always the fellow who has never made $40,000 a year, who knows all the reasons why you can't make $100,000.  If you have a dream, give it a chance to happen.  Don't let your brother in law or your plumber, or the guy in the next office, rob you of that faith in yourself that makes things happen.  Don't let the guy who lives on the couch and watches TV every night tell you how futile life is.

If you have that flame of a dream deep down inside you somewhere, do something about it.  And don't let anyone else blow it out.  Believe you can, and you will find you can.  TRY! You will be surprised at how many good things can happen to you!