Ashtavakra Gita

The wise man neither hates the unpleasant nor loves the pleasant, seeing both as equally the play of the one self

Explains equanimity toward pleasant and unpleasant experience as following from seeing both as expressions of the same single self, rather than as a discipline of restrained preference.

Chapter 18 revisits the theme of equanimity already raised in chapter 17, but grounds it here in a slightly different argument: the wise man treats pleasant and unpleasant experience alike not because he has suppressed his preferences, but because he recognizes both as manifestations of the one self that he also is. If pleasant and unpleasant are both the self's own appearing, favoring one over the other would be a strange kind of self-division, preferring one part of oneself to another. This framing gives the Gita's equanimity a metaphysical basis rather than an ethical one — the point is not that liking and disliking are wrong, but that they rest on a distinction, self versus not-self, the chapter treats as ultimately false.

Ashtavakra Gita