What is the main conflict in Please Look After Mom by Kyung-Sook Shin?

The novel explores how individual members of a family are traumatized by the sudden and unexplained disappearance of "Mom." As the narrative explores the loss, self-recrimination, and in some cases, self-discovery experienced in the aftermath of Mom's disappearance, it also considers themes related to the self-sacrifice of mothers, the relationship between past and present, and the shifting nature of identity.