Keltham would be so confused if he knew what Carissa was thinking! What is there to be curious about? Pain is ouch and bad. If it's severe pain you use mental disciplines to dissociate from it as much as possible. Masochists apparently get sexually aroused by it and submissives feel dominated by it, both facts entirely irrelevant to Keltham who is neither.
Dath ilani try to keep themselves simple, so that their theories of themselves can be simple without being false. If they seem complex to the eyes of another world, it's probably because the dath ilani are using some unfamiliar simplicities. 'Pain is bad' is a perfectly reasonable way for a mind to be, and correspondingly helpful simple thing for a theory of the self to accurately say.