Avengers: Infinity War - 14 Things You Probably Didn't Notice

8. How Thanos Knows Tony Stark

It's odd that Thanos seems to know about Loki being resurrected in The Dark World when he kills him and turns to goad Thor with "no resurrections this time", because it doesn't seem to make sense, but a later moment of awareness makes a lot more sense. When Thanos comes face to face with Iron Man, he addresses him by his name and Stark asks if he knows him.

Thanos' response is that he too is cursed with knowledge, which is doubly important. Firstly, it ties the characters together because both are haunted by the vision of what will happen to the universe without them and they've both been led to catastrophic events (one intentionally and one not) by their beliefs that they are the only ones who can save the universe from itself. The "knowledge" in that sense is that the universe will suffer if they don't take dramatic measures.

And more specifically to the Infinity Stones, Red Skull reveals that the Soul Stone “has a certain wisdom” - it knows every soul and can see them for what they truly are. The fact that Thanos then says that he hopes that humanity's survivors remember Stark suggests that he knows all of Tony's deeds and his purity of heart - a gift (or a burden) given to him by the Soul Stone.