Death Stranding EXPLAINED: All Ending Questions Answered
4. Sam's Real Family And His Connection To Bridget
This first Bridge Baby experiment is the context to the flashbacks Sam occasionally sees every time he plugs into Lou. The finale pieces all of these together, showing how Cliff tried to escape, but was ultimately cornered and shot. Making it back to the room with his wife, he slumps to the ground, manages to take the Bridge Baby out of its container, and cradles it in his arms.
Under Bridget's orders and with her own hand guiding him, Die-Hardman shoots Cliff dead, but in the process actually hits the baby as well, killing it.
This baby ends up on the shores of Amelie's beach and, distraught over what her other half's desperate actions have led to, she picks the child up and stops its passage to the afterlife. In her grief she revives the baby and sends it away from the Beach and into the waves towards the living.
However, it turns out this baby is actually Sam. The moment Amelie sent the baby back is the same memory Sam has throughout the story of his 'sister' meeting him on the beach, telling him it's time to go back home. Likewise, the scar on Sam's stomach that's featured prominently before then is from the bullet wound he received when he was a child, which Amelie patched back up.
Cliff was his real father and he was the original BB (which is why he had the flashbacks when he plugged into the other side), and when he came back Bridget raised him as her own, with his 'sister' Amelie visiting him in his dreams. The reason he has the unique ability to come back from the dead is down to Amelie giving him that power when she revived him, transforming him to a repatriate.