When I tell people I've written a (manuscript) book, it never ceases to amaze me how many people are amazed.
No, seriously. "Holy cow, you wrote a whole book? I could never do something like that!"
Yes you could. Anyone can. You learn the formula, pick bits and pieces out of thin air, build an idea, and VOILA!, book. Okay, it's not quite that simple, but that's more or less how it works.
The problem, then, is not coming up with the idea, (all ideas are essentially the same anyway,) it's not finding time to sit down and write it, (if you want it badly enough, you'll eek out a few minutes here and a few minutes there,) the problem is whether the would-be writer has a big enough ego to actually believe that anyone in their right mind would ever, EVER want to read their story.
So, yes, I did write a book, yes, I did happen upon an idea, yes, I spent 4 months researching Hinduism, Buddhism, Mysticism, Judaism, Islam, and myriad fringe belief systems, yes, I wrote - and then rewrote and rewrote and rewrote and rewrote - a book over about a 2 year period, yes, I studied plot structure and character development and all those other fun elements of writing, yes, I learned to self-edit (and it HURT), but most importantly, I've got an ego.
I may not be an Obama-style narcissist, and I may not have as much self-confidence as, say, a super model, but it's true that I must be fairly into myself - more self-focused than other people - if I could convince myself that someone would be interested in a story I devised.
It's true. If high school and its attendant miseries taught me anything, it was to believe in myself...that I have something to offer, even if everyone is oblivious to it. My heroine Jude learns the same thing (with the help of her friend Stacy): the only person who can determine Jude's self-worth is JUDE.
Is my sense of self egotistical? Well, egotism is preoccupation with oneself...to a fault. To the exclusion of others. Arguably, then, all writers are egotists. How many times did I lie in bed an extra fifteen minutes in the morning and command my children to fetch their own cereal because I was tired from staying up too late to write? How much did I spend on my websites? How often do I talk about my book? Oh, geez, I'm totally preoccupied with my writing. I hope it isn't to a fault, but the only people who can tell me if that's the case are my close friends and family...and they're too nice to tell me I suck.
Anyway, if you want to write a book, come up with an idea, set aside some time and get going, but for heaven's sake, work on your ego. It just might make the difference between idea and book.