I'll tell you why this makes sense to me: I've had a lot of jobs that required me to switch gears from one type of writing to another. If I tired of working on one project, I'd pick up another for a change of pace, then go back to the first one later. I nearly always had at least three projects in some stage of construction at any given time. So why not three novels? Number one is a light romantic comedy, number two a slightly more serious coming-of-age book, and number three is a sort of a spoof of the Dashiell Hammett-style hero (heroine in this case--a hard-boiled lawyer/sleuth). I'm finding that a little work on number three gets out a lot of hostility and stress so I can focus better on number one and two. BTW, there is a direct connection between books number one and number three: the spoof is included, partially, in the romantic comedy--it's excerpted as the book that my main character is writing. :) Fun!
We'll see how this shapes up. If it goes well, maybe I'll get all three done before my daughter goes to college (about six years from now). If it goes REALLY well, I may get all of them done within the next year or two. If it does NOT go well...I'll know by February.