One of the most interesting things about the tabletop RPG medium is how malleable it is. There are a thousand ways any mechanic, theme, or concept could be iterated, and rules can be made up on the fly to cover any number of situations as they arise. For me, this means that I keep looking at things I've done and asking myself 'how else could I have done this?' Sometimes this becomes a two-edged sword, as it means I'm never quite satisfied with anything I've done (even now, I'm contemplating revisiting all of my old classes and forging new versions of them integrating the new things I've learned since they were written).
This idea of reiteration becomes increasingly important when doing something as all-encompassing as Spheres of Power, and is also one of the reasons why designing this book is taking so much longer than originally anticipated. It's not enough to come up with a single version of these new mechanics, and I keep finding myself going back to the base mechanics again and again, asking myself to come up with new ways it could be done, and then I can take my pick of which variant plays better.
I think it wouldn't be a stretch to say that reiteration to this degree is something completely unique to Tabletop RPGs as an artform: Video games can be remade, or a book or movie can be adapted, but tabletop RPGs can be reimagined on a daily basis, and many games release 2nd, 3rd, or 4th editions of themselves as time and changing audiences alter the way the game is played.
Even Pathfinder, which famously has declared it doesn't like and hopes not to need a Second Edition does this; FAQs give updates on dealing with questionable mechanics, players come up with new ways of playing the game and post these rules online, and new products 'fix' old mechanics through the power of hindsight (my favorite of these is Kobolds of Golarion and Ranger Traps. I've never seen a player actually use Ranger Traps as they're universally considered underpowered, so KoG introduced a bunch of new, much higher powered versions. Technically it wasn't re-writing the old rules, but it might as well have been for the power change they introduced.)
Right now, I'm revisiting several of the spheres that aren't quite where I want them to be. There's a few places where something is broken in need of fixing, but sometimes it's about delving in deep and asking myself how a sphere feels, how it works as a playstyle, and if there's a version that not only would play better, but simply be more fun. Of course I'm running out of time and in some cases I just have to solidify things and move on, but the book, and the industry as a whole, is made stronger by reiterating things; it gives us options, and it helps us free ourselves from the belief that in such a malleable medium that there's a right way or wrong way to play the game.
As an industry, we're still under the D&D shadow; the D20 tradition (or F20 tradition as I've heard it called) is built on this reiteration of what, at its heart, is the same game of picking an archetype and going on fantasy adventures involving monsters and treasure. Even D&D itself has just reiterated itself once again, and as an industry we're all sort of waiting to see how this new iteration plays with audiences.
Anyway, that's just my thought for the day. If you'll excuse me, I've got to go and invent a new version of Creation to see how it plays.