An example of how destructive prejudices can be is to be found in John 9, in the story of the man who was born blind. "As he went along, he saw a man blind from birth. His disciples asked him: 'Rabbi, who sinned, this man or his parents, that he was born blind?' 'Neither this man nor his parents sinned', said Jesus, 'but this happened so that the work of God might be displayed in his life.' " ― John 9:1-3
This was the prejudice: the disciples find that the unique cause for the man's blindness was either his personal, or his parents' sins. They were in fact contaminated with this prejudicial mentality that was typical for Judaism: wherever there was human suffering, there was sin involved.
The explanation for this aspect is quite logical. Every little action has a reaction; every effect has its cause. If someone is suffering, that means God is punishing him/her for his/her sins.
Now there were some present at that time who told Jesus about the Galileans, whose blood Pilate had mixed with their sacrifices. Jesus answered: "Do you think that these Galileans were worse sinners than all the other Galileans because they suffered this way? I tell you, no! But unless you repent, you too will all perish. Or those eighteen who died when the tower of Siloam fell on them; do you think they were more guilty than all the others living in Jerusalem? I tell you, no! But unless you repent, you too will all perish!" ― Luke 13:1-5
"The same prejudice, according to which the person who was struck by sufferings, was in fact punished by God for a certain sin, also lived in the minds of Job's friends. Seeing him in great sufferance, struck by seven misfortunes, one more terrible than the other, the three friends remain silent for seven days, than they come up with a single solution: Job is a great sinner, and his misfortunes are nothing but divine punishments." ― (See Job 4:7-9, 15: 4-6, 22:4-5, etc.)
"Is it for your piety that he rebukes you, and brings charges against you? Is not your wickedness great? Are not your sins endless?" ― (Job 22: 4-5) This is the misconception of some people who pretend to be Job's friends.
To this unhappy friend, who is misunderstood by his closest friends, and even by his own wife, God in fact blesses and talks nicely of him in front of the entire universe: "Have you considered my servant Job? There is no-one on earth like him; he is blameless and upright, a man who fears God and shuns evil." ― Job 1: 8
Coming back to the disciples' question concerning the man who was blind from birth, if we carefully analyze their inquiry, we will clearly notice that it makes no sense whatsoever. How do they get it wrong? The man was born blind, with the incapacity to see the physical world. So it is not a disease that he got at a certain point in his life. He was born like that. Despite this, Jesus' disciples ask him: who has sinned, him or his parents? Why was he born like that? The normal question would be, when did this man sin to be born blind? Did he sin when his mother was pregnant, when he was still in her womb? When he was nothing but an "unformed body", like Psalm 139:16 says? It really makes no sense.
On the other side, if we take his parents' sins into account, which might have caused the child's blindness, God asked His people, the Israelites to confess the sins of their fathers and forefathers, this idea of sins having consequences was well implemented in their conception. Therefore, a sin (for instance unfaithfulness to God) had to be confessed, since it first occurred up to the generation that repented of it. "We and our fathers have sinned" was how in numerous occasions, the prophets who asked forgiveness for the county started their prayer.
However, the Holy Scripture also says: "The word of the Lord came to me: What do you people mean by quoting this proverb about the land of Israel: 'The fathers eat sour grapes, and the children's teeth are set on edge?' As surely as I live, declares the Sovereign Lord, you will no longer quote this proverb in Israel. For every living soul belongs to me, the father as well as the son; both alike belong to me. The soul who sins is the one who will die." ― Ezekiel 18, 1-4)
It is good to ask God before judging, in fact the Bible tells us that He, Jesus Christ is The Judge, and we are not to judge each other. God alone sees our capacities, and He alone can make a fair judgment.