A way to interpret the story and help understand the meaning is to think of the main prisoner as a teacher. The prisoners inside the cave are like students on their first day of school. Teachers
always try their best to help their students understand criteria that at first the teacher did not know until he or she was taught. However, teaching material to a group of students and making sure that the students understand the material is a skill that only certain people possess.
Another point is that even if the teacher is good at teaching, not every student is going to pay attention to what is being taught. Being able to have an open mind and learn new things is a choice that people have to make. The reason many people refuse to learn new things is because change can cause discomfort, anxiety, and frustration. The story displays the uncomfortable change whenever the main prisoner first goes outside. The main prisoner, from spending his whole life in a dim setting, is blinded by the light of the sun. The light causes his eyes to hurt. However, after being outside his eyes adjust to the light. The prisoners inside the cave are afraid of their eyes hurting, so they stay. The prisoners reject the new information given to them despite it coming from a former prisoner.
The unenlightened prisoners miss out on everything that is good outside due to fear of the temporary pain. To imagine something bigger is always challenging especially in adulthood. The prisoners spent their lives in the cave and accepted the cave to be their world. Learning new things can be uncomfortable, but the knowledge gained can be an advantage. The prisoners would no longer be trapped in the cave. The prisoners could develop relationships, adapt to the outside world, and have a greater understanding of life.