Supporting materials are necessary to turn an opinion into a persuasive argument. Being able to say something and have others immediately accept it as truth is a privilege afforded few speakers in few settings. In the vast majority of cases, audiences will not just want to hear the view you are asking them to accept, but also why they should accept it.
Supporting materials come in many different forms, from scientific evidence to personal experiences. Each is useful in different situations, but all are used to cause the audience to stop rejecting your idea as foreign and instead internalize it as truth.
Not all supporting evidence, however, is created equally.
EXAMPLE
Scientific evidence is absolutely necessary in settings such as an exam. Appealing to the emotions of the professor is unlikely to yield a positive result, while articulating and analyzing the correct facts is.Scientific evidence is used to prove that a set of facts or conditions is present in the world.
In other instances, more experiential evidence will help you connect to the audience on a personal level. Personal experiences and anecdotes are great for establishing an emotional connection with the audience. Being able to connect emotionally helps to mitigate some of the boredom that often accompanies appeals that are just facts.
Using non-scientific evidence comes with some dangers, however. Non-scientific information is not often generalizable. That is, just because there is a story (or series of stories) does not mean that they necessarily represent the broader truth. Some audiences are skeptical of non-scientific supporting materials for this very reason.
EXAMPLE
Using an anecdote of a boat sinking is unlikely to persuade most audiences that all boats sink. Attempting to use this type of evidence can actually weaken the appeal by decreasing your perceived reliability as a source.Source: Boundless. "Using Supporting Materials." Boundless Communications Boundless, 3 Mar. 2017. Retrieved 19 May. 2017 from https://www.boundless.com/communications/textbooks/boundless-communications-textbook/supporting-your-ideas-9/deploying-supporting-materials-45/using-supporting-materials-189-4189/