Jaykay is absolutely correct. Self belief, optimism and a can-do attitude are everything. Sure, one should spec out the lay of the land. But that's just to figure out which bits you will have to work harder to overcome, it's a pathetic excuse to not bother in the first place.
If I had done a SWOT analysis on every career move I made, I'd still be stuck in the UK doing a safe boring job, probably with a heck of a lot less money than I do now and none of the great life experiences. And lets face it, LIFE is what it's all about. Might as well actually live it.