Why is it necessary to have supporting evidence when making connections between events or issues in societies?

Historical thinking involves the ability to develop understanding of the past by making meaningful and persuasive historical and/or cross-disciplinary connections between a given historical issue and other historical contexts, periods, themes and disciplines. 

It necessary to have supporting evidence when making connections between events or issues in societies because it helps to defend your claim/argument. People will likely understand more and actually believe you when making connections.