Scientific research is a cumulative work, exposed to criticism whether positive or negative, and the prejudgment is accepting the result of a research as an absolute fact and adopting it without discussion, that is the negative adoption of previous studies
Without knowing what the previous research outcomes are, you are in danger that you will be researching something that is already sufficiently researched and your research would not be a contribution to the science. By knowing previous research you can build upon shoulders of previous and explore other aspects that were not researched yet or you can critisize and revise or reinterpret the current theories. So the ultimate answer is that the science is not a phenomena of an individual but a collective works, in which offcourse, you have to be critical and carfeul not to accept all of the previous propositions automaticaly. But in practice it is not possible to review everything, and you have to rely on previous researches for the sake of advancement in science. That is why metodology is important and confirmation of theories by others.