How Long Does It Take To Write A Novel?

I was warned about this. Some authors takes weeks to finish a work. Some take months. Some take years. I didn't think I would be one of the latter.

If you had told me when I first started The Owl & The Eagle that two years later it still wouldn't be finished, I would have balked. Yet here I am. There are days when I worry: is two years too long? Almost every day I think of something to add, subtract, or tweak in my book. But I worry: is this NORMAL? Do published authors go through this too? Or is this a sign I'm not cut out for writing? Any clue, fellow authors?

On a side note, the next excerpt (sp?) from O&E is coming up. It's a preview of Themistocles and the Athenian embassy in Corinth, when the allies meet to decide how to fight the Persians. It doesn't go the way Thems wants it to at all...