Just terrible memories growing up in the Borg. Especially when it came to the holiday season. Being left out of everything the class did or being told who you could or could not befriend.
On top of that were those horrible, hateful, dreadful magazines and books. Those images of people being burned alive at the big 'A'. Images of the ground swallowing people up by the dozens, fear-mongering conventions. Just terrible, terrible things for a child to endure at such a young age. Terrible childhoods of the people in the Borg.