P, being comfortable alone is like repeating a one-note melody... being with other people, in all degrees of relationship, allows for chords, harmonic & bass lines that weave in & out of the melody... with multiple rhythms... etc for a whole symphony. Sorry that's not a direct answer to your question; not sure I have much better than that to describe what I mean. By myself, I have only my own perceptions, thoughts, knowledge, history and emotions... interacting with others, sharing, talking, doing things... expands that "universe" or "story".
All alone in my own story, I feel like Clint Eastwood in Josey Wales when he says: a man has to know his own limitations. All alone in my own story, I felt unable to do a damn thing about those limitations... I was simply working with too small a data set... and once I found a way to interact with others outside my normal comfort zone... the data set grew; the sample size increased; and the range itself even seemed wider. All alone in my own story, my definition of those limitations - my perception of them - were all WRONG and I couldn't even know that... because I was only seeing, knowing, perceiving, experience the inside of my own story-bubble.
I know I'm probably not making a lot of sense... it's a hard thing for me to put into words; not sure if pictures would help - haven't thought about that until now.
SEA: I just finished a book similar to the one you described, that is "feeding" some of my creativity again and probably adding some shading to what I've said on this thread... and that you might like too. It's The Magicians - by Lev Grossman. It started out seeming like a Harry Potter story for adults; but by the end of it, I was finding and being touched by some very deep themes that still haven't completed reached the verbal part of my brain yet. I haven't read a novel like this, in some time (have been a lifelong voracious reader). I dove in and finished it in 2 days - and literally couldn't put it down. It was one of those books I'd picked up out of a table full somewhere... added to the stack... packed up in boxes... moved... and finally decided to open, last week. Even if the themes I see in it don't resonate with you... it was still quite entertaining and a good distraction while we have a pretty grey & rainy week.