The term prejudice implies, that people come to a judgment on a subject before learning about the reality, or forming a judgment without direct experience. When applied to social groups, "prejudice" generally refers to existing biases toward the members of such groups, often based on social stereotypes.
If no amount of experience entitles a person to a viewpoint, there can be no objectivity. Judgements based on experience may, however, be coloured by prejudice. If a person has developed the concept that members of one group have certain characteristics because of a negative past experience with a member of that group, he/she may presume that all members of the group have such characteristics.
In other cases, it may be a matter of early education: people who were taught, that certain attitudes are the "correct" ones may form opinions without weighing the evidence on both sides of a given question. Many prejudicial behaviors are picked up at a young age by children who imitat their parents' ways of thinking and speaking, with no malice intended on the child's part.