Protecting Themselves?

Taylor states in the last sentence of Chapter 5, "Pride and Anger," that the resentful keep their feelings to themselves as "a form of self-protection." This surprised me in that Taylor first gave this primary reason in the last sentence of the chapter. This made me somewhat confused as to what Taylor truly beleives is the motives of the angry, or at any rate, the resentful.
Taylor initiates her discussion of the resentful by stating that they "feel themselves to be constantly undervalued, [although] they keep this feeling to themselves." Taylor, at this point, does not state that they keep this feeling to themselves for self-protection.
It may be harping, but I feel that why exactly the resentful do not share their feelings, thus initiating the vicious cycle of resentment, is an important issue to clarify (and consequently deserves more explanation than a two-word afterthoguht at the end of the chapter).
If Taylor is correct in stating that self-protection is the main reason for why the resentful do not make their feelings known, then what is the cause for the agent's desire for self-protection? For argument's sake, let's say it's fear at having one's self be shown to be worthless, as Taylor seems to imply in the chapter. Then what would this fear be attributed to? A lack of confidence in one's self-esteem? Perhaps knowledge that one's self is of less worth than others'?
The former explanation seems more likely than the first. If that's the case, to what can we attribute the lack of confidence? Poor self-evaluation?
By cutting off the explanation for why the resentful wish to protect themselves, Taylor has left incomplete an otherwise impressive explanation on anger and resentment. But the failure to explain the roots of resentment, I feel, leaves an important part of the topic open. By better investigating the start of resentment, we might be better able to understand resentment itself, which could be useful in understanding anger as a whole.