Google is not a human. When indexing thousands of web pages through the Google Search algorithm, Google often finds the same content of different pages of your website. Duplicate content is harmful to your SEO. It can lower the rank of your website.
Duplicate content issue gets worse when people interlink different versions of the same content
As you all probably know, internal links are a healthy way to build authenticity of your website. However, when you interlink different versions of your website pages that have the same content, you lose the hard-earned respect from Google. Google takes action, and your website will rank lower than before.