If your goal is to have a "sticky" site that delivers a message to millions of visitors per day, you need to figure out how long you're willing to work towards that goal then figure out how quickly your site needs to grow. If you follow tried and tested methods like writing interesting content that people enjoy and getting links from other sites, all it should take you is time. But it will take a lot of time. 10 hours of work will almost never generate millions of real visitors per day, but it might get you another one, 10, 100 maybe even 1000 if you're lucky. If you combine a real expectation of time you're willing to invest with balanced goals in terms of traffic, you should end up a happy webmaster.
The main site I run is an information web site. My goal is to get as many people to view our information/brand. That means unique visitors are key for me. That's what I measure for growth. However for someone who sells something, sales are the bottom line. Whether they come from lots of unique visits or lots of repeat traffic is a secondary measure for them. Number of sales will be the yardstick by which they measure their growth.
Once you have a clear idea of what your goals are, then you can decide what metrics to use to measure your growth.
To summarize, the success of your site is really going to depend on what you want to get out of it and what you want to put into it. It's all relative, there's no real set formula for success except the following:
(your effort) * (your experience) * (your knowledge) * (opportunity) * (luck) / (your expectations) = level of success
There's a bunch of variables in this equation that are under your control. Be sure to take advantage of that fact.