In this video, Matt reveals that "something like 25-30% of all the web's content is duplicate" and that Google accepts that it's something that happens, for example if you were to quote a paragraph from another blog on your website. From this point of view, Matt points out that Google does not automatically assume that your website is spam unless your website is composed mainly or entirely from content found elsewhere. That said, the problem arises when your website is not the first to publish content, since Google will group duplicate content together and only return the original version.
The take-home message from this video re-enforces the "content is king" ethos of good Search Engine Optimization (SEO). For maximum organic search-engine traffic, it's important that you publish high-quality original content on your website and that it's OK if it gets republished. In the event that you share your content or it is frequently quoted or copied, it's also very important that your website automatically "pings" Google to re-spider your website's XML sitemap - therefore alerting it that your version is the original.