"The Solo Partner" says that the distancer will believe they can get more out of the relationship than they are willing to put into it. When the pursuer stops pursuing, they feel this loss and want it back, so they'll do just enough to try to restore it.
This was the quote that struck me from the chapter as well. It basically means that at whatever level you decide on for your pursuing, their reciprocation input will always be less. And it's not just a lack of understanding, like Men/Mars and Women/Venus issues. It's a lifestyle for them. I know (I've proven) for me, that just doesn't work. I'm worried for you because you clearly want more, AND you're willing to give more, but your W isn't. Period.
