I read a lot about successful people.  I also think a lot about people who aren't as successful as they could be.  My theory is that if I can determine what makes or breaks success then I can either emulate or eliminate as the case may be.  Recently I've become convinced that I've found at least one piece of the puzzle and it has survived back-testing against both the success stories and the group who falls short.  The entire concept can be boiled down to 3 words:

Commit and deliver

I originally spent some time thinking that it could be boiled down to 2 words "commit" and "deliver", but it turns out that the "and" is critical.  I've worked with lots of people who commit, but then fall short on delivery.  These are usually excuse artists who are more adept at explaining away success than they are at pursuing it.  The excuse artist won't see non-delivery as failure, they'll just explain how they could never have been expected to deliver . . . despite having committed.

I've also worked with people who deliver, but never commit.  I'm sure everyone has worked with folks like this.  They're the wafflers, the ones who caveat everything to the point that they cannot be held accountable, they're the ones we often call "slippery".  They will, however, sometimes deliver something of value and then never let anyone forget it.  These people have entire catalogs of accomplishments in their head, but have never failed and never been wrong.  If you think that they have, they'll be quick to point out that in the particular case that you mention they never said they'd deliver, they said they'd try or they'd see what they can do or that it might be possible.

I'm pretty fortunate to have worked with a few people from the final category.  The ones who commit and deliver.  These folks are great to work with.  They say, "I'll do X" and X gets done.  Not always as smoothly as originally thought, not always as quickly as originally thought, but it gets done.  It gets done without fail.  No excuse, no ambiguity about whether or not they're on the hook for delivery, just straightforward "it will be done".

There may be other factors that shape and size your success, but I guarantee that if you simply commit to doing things and then deliver relentlessly that you'll succeed.