Book Writing

So I am writing a book. A book of Economics, to be precise. No, I am not an Economist per se. I took one class in Economics in 9th grade. I am a Geophysicist (I have a Ph.D. to prove that one) by training and some kind of analyst by profession (I think. Well, I really hope so). 

So I am writing a book of Economics. Because I find it fascinating. Because I think I may have a different point of view. But I don't know if that point of view has been worked on before. If they already have some fancy term for it.

Yet, I am writing a book. And I plan to publish it. I think it's a good idea. Well, sometimes I think I am in over my head on this. 

Yet, I enjoy writing the book. Well, most of the time. So I am going to write that book and publish it on Kindle. I will let the market forces do their job.

PS: How do you figure out that your book is done? I mean I can keep writing and keep adding something or the other to it. How do I know wits time to stop and publish the book?