The Red Thread

I'm having trouble finding what Italians call the filo rosso - the read thread. The thing that connects your thoughts together in a coherent manner; that goes from one page, one author, one century to the next.  I embarked on my proposal journey with the intentions of, initially, writing one chapter each on four authors; then I found myself in the weeds, considering writing on only one author, but I felt really uncomfortable doing that; now, I've decided to write on two different authors, four aspects or relationships of their writing that can be shared to a certain extent.

But that red thread...continues to elude me. Well, not entirely. I feel like I have the thread in my hand, and I'm just having a hard time threading the needle. It looks like I've perfectly lined up the end of the thread with the eye of the needle, but I keep losing it right at the moment that I should make contact.