Once again a background story about Seven's life as a Borg drone. We meet other drones who once served in the same unimatrix as Seven and were connected to each other in this collective, also with Seven. They too were able to free themselves from assimilation, but are prevented from living their own lives as individuals by the still existing connection between their minds. The three share every thought, every feeling, every memory with each other.
With Seven's help, they try to separate from each other, but it doesn't quite go according to plan. In flashbacks, the viewer learns that after a space capsule crashed, Seven prevented these drones from isolating themselves from the collective. This is a strong character moment for Seven, because from her current perspective - as a drone whose connection to the collective has been severed and who is now an individual - she knows that what she did was wrong back then. She took away their freedom, a freedom that she can now live out herself.
When she is faced with the same choice again at the end - individuality or collective - she is torn between which standards she should use to make her decision. Is it more moral to preserve life at all costs as the doctor says, even if that means merely surviving as a mindless drone in a Borg collective? Or is living a responsible life as a self-determined individual the only way out as Chakotay says, even though this life would only be very short in the end? I think Seven makes the right decision and at least makes up for some of the guilt she took on back then.