Bias in Research Methodology Design

This week's peer review made me realize just how complex research methodology can be, especially in terms of the design. Those in charge of the study have to make sure that their methodology tests everything they intend it to and that these tests are reliable. The problem is, every researcher approaches the study with a bias, and this can affect the results. It's one of those things that can't really be avoided, but it can sometimes be argued that a bias can be good for the study, as it might bring a new and unique perspective. However, sometimes the bias can completely distort a study because the researcher had something particular in mind and, subconsciously or not, designed the study towards that bias.
Biases are something that every researcher has to deal with, but it just becomes a question of how aware you are of your bias and whether the bias affects the research design in a negative way.