Find a source that helps you understand Plato's simile of the line, cave, and sun
Plato source

After reading this article I discovered that Plato's law of forms is very much important to understanding his simile of the line, the sun and the cave. In the simile of the line, everything above the divided line is true knowledge and includes the knowledge of the forms. The forms are the concepts or total ideas of thing in the world. The shadows in Plato's allegory of the cave can therefore not be considered true knowledge or knowledge of the forms. These shadows are instead allusions and misrepresentations of reality. Without the knowledge of the forms, you can never know the nature of reality.
The simile of the sun the is mentioned by Plato in order to draw a focus on the idea of goodness or justice. Without the sun the the eye would not be able to see. Without goodness the truths of the intelligible world would be inaccessible.
The simile of the cave is presented in order to draw attention to the importance of Plato's theory of forms. The prisoners in the cave are depended on their sense of sight, which, according to Plato is undependable and not a source of truth or the intelligible world.

Plato's tripartite soul and more!

Here's my collage of Plato's view of the soul as compared to other versions of the soul. Some of the images in the collage are metaphorical, or are representations of the soul. These images are not meant to be interpreted directly.

Based on Plato's version of the soul, how does he see the human condition?
Plato's version of the soul is broken into three parts: reason, passion(appetite), and spirit. The role of the reason part of the soul is to rule over and control appetite and spirit. The fact that Plato had to create a whole part of the soul in order to control the appetites of man suggests that Plato had a negative view of human nature. Without reasoning to control the appetites, or desires, the soul would not be harmonious or just. The fact that reasoning controls the other parts of the soul also suggests that Plato thought that humans needed to have extreme control over their bodies, and focus on their mind through reasoning. This would make sense because Plato obviously was a philosopher and he therefore held the view that education and training of the mind was necessary in order to obtain goodness through justice or harmony in the mind.

The other souls in the collage can be considered to have been influenced by Plato's version of the soul. Most of the souls in the collage are separated into more than one part, an idea that can be traced back to Plato's three-part soul. However, the souls in the collage have different parts that Plato's. Plato combines his highest, most spiritual parts of the soul, reason and spirit, with corruptive appetite.  However, the Christian and Sikh souls do not specifically address the damaging parts of the soul, like appetite. This would suggest that these versions of the soul have a more positive, hopeful opinion of the human soul and condition.

Plato Propaganda

According to Plato, propaganda can be considered any type of ad because all ads attempt to sway your opinion. Whether the ad is trying to get you to buy or do something, it changes the opinion of the viewer. It is this change that Plato's Socrates considers propaganda and witchcraft because propaganda evokes emotion which is secondary to reason and the mind.

Here is the image I used in my response: 

Plato's view of the human condition

Assignment: How does Plato view the human condition?

Before answering the question directly, it is necessary to first describe the key term in the question just as Socrates or Plato would.
The human condition can be described as all of the parts of existence that help distinguish the human being as unique from other species.

Given this definition of the human condition, Plato would have viewed the human condition as being inherently set up for failure. This is shown in the Republic as much of the book describes rules to govern humans in an ideal society. If Plato already had a positive view of the human condition, he wouldn't have written out guidelines to correct the mistakes. Rules are created for those who break them. In creating rules to live by Plato is anticipating challenge to his ideal way of living and therefore he is also anticipating that some humans will break the rules.
However, just because Plato thinks humans might break the rules doesn't directly imply he considers the human condition as being set up for failure. If humans break rules there must be reason for them to do so. Here Plato would point out the temptations in life that are especially apparent when describing the qualifications of the guardians or ruling class. According to Plato, the guardians cannot be corrupted in the slightest. This means they can't have wives, wealth or property. To Plato, these temptations only bring trouble and will eventually tear the society apart. If temptations are considered part of the guardians' trial then they are also considered to be part of all humans, since guardians are humans and all humans experience corruption too. This means that the human condition, according to Plato, must include certain challenges, or temptations thereby making it imperfect and inherently set up for failure.