This article by Jane Friedman is an interesting one, because it looks at other motives besides money. Do you want the validation of working with a traditional publisher? Do you have a lack of patience? All good points to consider when deciding whether to self/trad publish.
But, of course, some of it comes down to money:
On the issue of earnings
Perhaps the biggest argument offered in support of self-publishing–at least within the self-publishing community itself–is that you will earn a lot more money than you would with a traditional publisher. That may be true. It’s possible to sell far fewer copies as a self-published author and yet earn more than a traditional deal would pay you; it’s also possible to sell more copies as a self-published author but not earn as much as a publisher’s advance and royalties. It all depends on the book and the type of deal or contract you’re offered.
The success rate for self-publishing is really not that different from traditional. A few authors end up as bestselling superstars. Some authors do very well. And the majority do not make a living from it. Self-published authors may find that marketing and promoting their book is much tougher than they imagined. Self-publishing careers typically take years–and four or five books–to gain traction and produce earnings that are meaningful. Are you committed to producing more work, and marketing that work, month after month and year after year?