If that person goes into a new business venture with the slightest doubt of themselves or the actual business, they've already given up in their minds.
And all they need is an actual physical excuse of not seeing what they wanted or getting what they wanted in a certain time frame to lose all motivation and lie to themselves saying "Oh, this isn't going to work. It's not for me! I just don't have the funds to invest!" and so on and so forth.
A true desire to change one's current situation starts from inside first, then all else will fall into place.