The first thing that you should do in this question is identify a word that fits the context and try to identify a synonym for the same sentiment. Here, the best fit is ‘basic’, which essentially refers to an in-born instinct of a person to defend himself when criticized. This sentiment can be best replaced in the blank by primal, which means having existed from the beginning; in the earliest or original stage or state.
Capricious- unpredictable or volatile
Pragmatic- Practical and realistic
Hardnosed- realistic and determined; tough-minded
