I have absolutely no idea of what learning process social interaction facilitates, but I can give you at least a really silly example of what sort of thing you do get when learning something from a person with more experience on the given subject. Everybody has seen at some point the basic expressions for the maximum and the minimum of two given real numbers $a, b \in \mathbb{R}$, say $max(a, b) = \dfrac{a + b + |a - b|}{2}$ and $min(a, b) = \dfrac{a + b - |a - b|}{2}$. I had always found it hard to remember the formulas. Well at one time I just realized that both formulas are completely obvious if you think of them as saying that for instance, if you want to get $max(a, b)$ then you just need to first step on the mid-point between $a, b$, which is $\dfrac{a + b}{2}$ and then you just have to "walk" from there half the distance between $a, b$ which is $\dfrac{|a - b|}{2}$ and similarly for the $min(a, b)$.

So at some point the chance came that a friend of mine needed to use one of this formulas and he said, "Oh but I don't remember exactly how they were". So I explained to him what I just said and he told me that he had never seemed them that way and that now he was sure he will not forget them.

My point is that this is exactly what you can get from an expert or from someone who has already thought about what you are learning at the moment, the hands on experience and the insight they have is what is most precious about this social interaction you refer to, it can give you the necessary ideas that you may not get from reading a book. You'll usually get more from this than what you get from a book or a paper. Obviously everything complements the other part so of course you can't expect to "be like Grothendieck" and learn everything directly from other people and you'll have to start taking the math from books, papers, wikipedia, etc. In a way I think of this as an aid in connecting the ideas I get from reading a book.