Its a big subject with lots of different elements to make the answer!
You could look at it from a different angle.
99% of people have a 'great' idea for a site
.9% will make that site, but then get discouraged at the fact that making it is the easier part, making it work is where the hard work starts...
.1% will get through their struggles and start to see a site that works.
This applies to Dolphin, Joomla or any other site script...
How much it works though, will depend on who its aimed at, if there is a need for it, if you can support it (financially, time, content and technically), if you have a business plan or if its just left to organically develop, if your site has good income streams, if it has a number of income streams, then a good helping of LUCK and HARD WORK!!!
Some will succeed, most will not.
However, what you do from there is just as important.
You have to then ask yourself, if you are the kind of person who gives up when faced with difficulties, or if your first idea does not work....
or
if you are the kind of person who will see what some would call a 'failure' and view it as a necessary step in getting to the next idea you have then working that through...
eventually, your ideas get refined, your skill base grows, and you will find the right idea for you that works.
Its not so much about Dolphin, its about the person behind the site that will be the biggest factor in your sites success or not.
The majority of successful entrepreneurs have had more failures than they have successes.
You have to learn to 'fail forwards' otherwise you don't go anywhere and your ideas become dreams...