I'm not sure I understand the distinction between determining our choices and determining our reactions to our own choices. Can you elaborate? Solomon doesn't justify the point that much, he more uses the claim in service of a wider argument that we often trap ourselves in our own self-conceptions without even realizing.
I agree with that argument. Yes, we can trap ourselves in a self-conception. So he's arguing that the essence of self" is a self-conception that can be delusional. I can see that. It would be hard to realize or see that we have created a self-conception that is looking at ourself through its self-created lens. I'm suggesting that we make all kinds of choices, good ones and bad ones. Choosing Coke or Pepsi, to sleep on a couch or on the floor, to support candidate A or B -- those choices show our preferences and our thinking which can be as "fluid" as Solomon says. But our reactions to good and bad choices can potentially be less fluid and more consistent and show an "essence of self."