It is hard to wrap your head around, and only the engineers behind the purple curtain at google really know.
That said, here is my understanding. First define it.
Duplicate content = content on your web page that is contained within any other web page within google's index
How strict is Google's objection to duplicate content? One duplicate? Many duplicates?
I mean, if I post on my blog and then post that same article on one article directory, will I be penalized? How about two article directories?
And how does Google punish us for putting out duplicate content?
Not that strict. There is a level of fair use when it comes to copyright for example. A snippet of a quote may be included within a news article then replicated thousands of times over different websites.
On the other hand, if you make a 1:1 copy of this website and then promote it as your own I would guess you won't get far. Will that "penalize" this site? Probably not as anyone can do it, and as a site owner not something I control.
That comes to the word "penalty". I don't think that is how it works. I look at it from the perspective as it is not going to help you. The punishment is the duplicate content is just ignored, imo. A waste of time when your time could be sent adding new unique content of value.
Regarding the article sites, may not "Penalize" you. But may be totally spinning your wheels to go nowhere. My advice, if you want to try article directories then write unique content on your website. Then when publishing to other websites also write unique content. If your site is authoritative and of value, then can you link back to it?
So, in the end you might have the impression unique content is best. And duplicate content is just ignored. You choose where you want to spend your time, but don't have anxiety that you are going to "penalized" if you have content that can provide value and you want to quote it.
Have doubts, always easy to understand when you test it for yourself.