Bias

When looking at a source one has to look for Bias. Bias is someones opinion and when you are writing a paper or essay you don't want someone's opinion in your factual essay. If someone gives you facts but they also have their opinion in it too then you use it in your paper, your supposed factual paper is now tainted with someone's opinion.
Bias can ruin a paper easily. If you have bias in a paper in can warp a fact into a lie. When someone notices that there is a false fact in the paper then your whole piece of work is called into question. Another example  of Bias ruining a paper is when it offends someone. Someone who has an opinion against a certain group of people for example could sneak in some racist material into a fact. When you use that fact you may not notice the hurtful intentions behind it and you may inadvertently offend someone.
Overall one should look for bias when doing research to make sure that when your paper is done it has no ones opinion in your writing and just facts.