Confusion in rel="canonical" in wordpress posts

As far I understood rel="canonical" is that it's used when you want to indicate the original source of an article in the duplicate page.

But in wordpress what I see is that in rel="canonical" tag the link that it shows is the same link of that post it self. which really confuses me.. I thought it should have been in the blog pages if at all it needed to be used.. :/

Poster :