The Case of the Missing Theme

If I had a chance to sit down with the Pulitzer Prize winning author Elizabeth Strout I would have several inquiries in which I would like to see answered. However, one such question regarding her 2008 novel Olive Kitteridge has meddled itself into my thoughts since finishing the book and even during the story itself. "What is the overall theme of your novel"? It seems such a basic, shallow, and unspecific question however I can not seem to pinpoint an overall purpose for the story. The brunt of the issue lays within the way Strout writes: thirteen separate stories within themselves each with ostensibly little to no underlying connections with one another. Aside from basic plot developments connecting from one story to the next unearthing a carrying over theme seems nearly hopeless. Given, each story has its own set theme which presents itself without much need for analyzation. For instance, the theme of Ship in a Bottle: "sometimes one has to sacrifice what they think is right choice for the betterment of others". Strout proves this theme when Winnie's sister runs off with her boyfriend instructing Winnie not to tell anyone. Consequently, Winnie "almost cried" due to her yearning to tell her parents, and second guessed herself thinking "they could still do it [get her sister], she was still here" (197). However, Winnie does not give it up until her sister had already left, validating the theme. Likewise, other passages have their individual themes, take A Different Road  for example, Strout includes an individual theme of how "One needs to cherish everyday because anything can happen". This exemplifies itself in how quickly a normal day turned into a life or death situation for Olive. When at the hospital for a surprise check-up "A tall man holding a rifle" and a "person in a blue ski mask" take her and her husband hostage (113). They end up making it out alive but not after they have guns pointed at their heads and threats made, this external conflict supports the theme associated once more exemplifying how each story has its own theme. However, therein lay the problem for me. I could not help but search for a connection, a vague similarity, I expected that the last story would provide some sense of closure. Unfortunately the last story seems to posses its own theme as well. Not to mention no connecting of the characters or events took place at the end either which I could bear, but still the question keeps nagging me. Without a universal theme, however ambiguous, how can there be a true purpose? So please Elizabeth Strout, drop me a hint here, what did you intend for the universal theme? Unless each individual theme somehow harnesses a purpose which I have yet to ascertain.