I think this may be one of those questions that need to be better defined before they can be answered. What do you mean by "successful moments"? I would have different answers for different definitions. For example, I would consider the ribbon-cutting on my brand-new, me-designed agency as a "successful moment", but that had many, many, many components leading up to it. Tenacity would indeed be a leading reason for that "successful moment."
But if you mean something narrower, something more defined and finite, my answer might be different, more like patiodog's. If I have a specific challenge in front of me -- say, meeting with two extremely objectionable members of the committee of which I am president to try to get them to stop warring -- I have a, hmm, zone maybe that I purposely go into. It's kind of a clarifying thing, I like what patiodog says about mental static. Just a deep intake of breath, slight adjustment in posture, intense focus coupled with physical relaxation, and whammo. Hard to describe, but the key thing in that mode is that information is received, swirled around, and (-- ack, ASL sign, can't think of English translation -- synthesized? Sort of.) synthesized so that solutions are readily visible.
Gawd, that made no sense. (NOT in that zone just now.