Board Thread:Questions and Answers/@comment-27491885-20151228162741/@comment-35615238-20190131210300

For all we know, both of the skeletons could have been born at the same time. But Sans does act a lot like an older brother, in ways like keeping Papyrus from the truth about resets along with not saying everyone died in his neutral ending, as he doesn't want to destroy his optimism and kindness.