Here are two identical articles published on different high-traffic websites:
1. How Our Brains Stop Us From Achieving Our Goals (and How to Fight Back)
2. How Our Brains Stop Us Achieving Our Goals and How to Fight Back - The Buffer Blog
Both articles are indexed by Google.
LifeHacker reposted the article under author's name as a guest post after the author asked them to do so. Now, bear in mind that the author (Gregory Ciotti) is actually being linked to by many SEO experts as somebody who knows SEO stuff and obviously people at LifeHacker are no slouches either, therefore, I feel it's safe to assume that both these articles are safe in the eyes of Google.
With that being said, how is that not a duplicate content?