Why can some start and other's not?

This will probably be a open-ended question, considering that it might be very opinionated... But I'm curious to hear from the community here-- why do some fail at getting past the conceptual phase of their venture and others seem to be quite good at it and enjoy it? I'm especially curious about the psychology and the traits you feel make an entrepreneur successful in at the very least getting off the ground.

I know first hand that experience is a big one. Tiny successes build confidence, which make more successes. I don't think that is all there is though.

Ever heard about E-Myth?

From Onstartups :

Years ago Michael Gerber coined the
the term E-Myth, referring to the
entrepreneurial myth of people going
into business to do what they love,
only to realize that 80% of the
business has nothing to do with their
passion--but instead with building and
running a company.

This often results in one of two
outcomes: The founder hates his job or
the business fails--usually the former
follows the latter quite closely.

Many times the "block and tackle" type tasks that starting & running a business requires overwhelms the startup. Outsourcing this can help (as suggested in the above referenced onstartups post) but that only brings you so far - it's not all "build your super awesome idea and customers come rushing in" type of fantasy that gets promoted.

But, if you approach startups with the right perspective, expect to do a lot more than you initially expected, and can read / correctly interpret eemingly conflicting inputs from multiple sources, you have a chance to gain some traction. Whether that traction meets your definition of success is up to you.

See also this post for theories about why some startups fail.