Good writing is about change and overcoming challenges to achieve a goal. This is as true in fiction as it is in narrative nonfiction.
However, it does not generally make for interesting writing to show someone working through problems with a therapist or in some very open and intentional way. We do this in our lives, but where there is dramatic tension is when a simple route is not an option.
There needs to be the obvious tension of can the character achieve his or her goal. In one book that could be does the person survive a life threatening challenge? Or it could be, do they change in order to find happiness?
In either there is the obvious tension, but there needs to be an underlying tension. This is where a person's flaws come in. Alcoholics and other addicts in recovery understand the natural tension between a person's desires/intentions and their flaws. Flaws are what make achieving our desires/intentions next to impossible. Flaws make internal, personal change very difficult.
So not only does the protagonist work against an antagonist, but they must also work against their own personal flaws.