The reasons for prejudice vary. Some are related to historical events.
Often, prejudice is based on ignorance. The solution is education, but many people choose to remain ignorant, as their prejudices often make them feel superior.
Victims of a particular kind of bullying may go on to become bullies themselves. In the same way, if a person has been a victim of prejudice, there is a chance that they will come to hold similar opinions about others.
A person's upbringing may cause them to become prejudiced. If parents had prejudices of their own, there is a chance that these opinions will be passed on to the next generation.
One bad experience with a person from a particular group can cause a person to think of all people from that group in the same way. This is called stereotyping and can lead to prejudice.
The media has a powerful influence on people in the 21st century and can often be responsible for promoting a stereotype of a particular group.
Scapegoating is an example of a specific type of prejudice. A person or group can be blamed for the sins or wrongs of another person or group. For example, in 1930s Nazi Germany, Jews were made scapegoats for the country's economic difficulties.