Selection of goal then denying it myself

I have a problem of over thinking , which creates a huge disturbance in moving on for me upon a path to my destination. Whenever I started my journey , from beginning I was having a great inspiring ideas in mind , so that I was using to go ahead over a path following my destination of a goal , but at the centre of path , my mind behaves totally opposite of the ideas in beginning , it screams much more than the noise of polluted areas.And then at last I accept the objection of mind . And heart also makes me blackmailed with my mind. I'm getting very much frustrated that time. This problem spoiled my career . I'm now totally disappointed by myself about life. May I know , what is my problem and its solution as well.