They likely don't find it unbearable if it's normal. Stagnation was the largest part of human history. Only since the Renaissance has progress accelerated substantially. Before then, the life of the children was about the same as the life of the parents and grandparents. Life was governed by tradition. Everyone had their predictable role to play. Being unhappy about "stagnation" wasn't an option, as anything else would have been outlandish science fiction, which didn't exist.
Universal human condition, I guess. If we're going to persist in being miserable, might as well keep to ourselves and not screw it up for the other forms of life on this planet.