i think being determined and positive is one important facet, but not the be all and end all. thre are so many more factors at play but mindset is definitely one of them.
what are your unresolveable worries?
do you have support from yoru MW, DP etc...
there is also an element of luck involved, for instance , if your baby is in a really bad position, and you need another c.section, mindest won;t have any effect on that.
i was absolutely totally determined to have a VBAC, to the point of obsession. but i had a straightforward normal birth and it inspired me to become a doula.
a lot also depends on how supportive the hoispital are, if you feel like you ought to have a VBAC, rather than wanting it, at the first hint of oppostion, you won;t want to fight for it, so, i suppose that is a good indication to you of whether you do really want a VBAC, IFYSWIM
a lot can also depend on why you had a c.s first time