I've been thinking about this for some time. The short answer is simple... No, it's not.
But a more detailed answer is this: It's the only place to start and it's pretty much a necessity. Only pretty much you ask? Well yes, as sometimes a unique and cracking idea can be enough in itself. For example there are plenty of screenplays that have been re-written beyond belief by other screenwriters, because the idea was great, but the execution was massively flawed. Anyhow what is certain is that a great idea, well executed is a brilliant place to start (obvious I know).
But then you get into the more difficult area of promotion. At the end of the day if nobody knows it's there... nobody is going to buy it. So as a seasoned author (well my book has been on sale for two weeks now)
1) You definitely need to promote your work (been doing that and will continue)
2) With all the promotion - where does anyone find the time to actually write!
3) People have been great, from my friends, family, acquaintances to complete strangers who I've 'met' via various writing forums and who shared their advice and experienced because of their shared interest in books; it's made me realise that there are some truly great people out there - so a sincere thanks.
So how do you become successful - well that's the content of another blog for another day me thinks.
Either write something worth reading, or do something worth writing; Benjamin Franklin.