“A witness is someone who has, who claims to have, or is thought, by someone with authority to compel testimony, to have knowledge relevant to an event or other matter of interest. In law a witness is someone who, either voluntarily or under compulsion, provides testimonial evidence, either oral or written, of what he or she knows or claims to know about the matter before some official authorized to take such testimony.”
Its not just in courts of law that you need witnesses to support your case. Every presenter needs to bring on their witnesses also. Audiences need evidence before they make their minds up.
Give them facts, statistics, anecdotes, images, photos and quotations.
Win your case!