The Sidekick

Poirot had Hastings, Laverne had Shirley, Shaggy had Scooby, Sherlock had Watson, Lucy had Ethel, and I've been thinking about the sidekicks, straight "(wo)men", and enduring friendships in both fiction and reality.  What is the bond that glues them?  Would I put up with Sherlock or Poirot as Watson and Hastings did?  Why did Ethel always back Lucy in one way or another?  Why do these matchups appeal to us?  I've had friendships that have waxed and waned for well over three quarters of my life now. And I try to bring what I've learned about those friendships to the page in a fictional friendship between Lorna and Annie.  Annie, like Watson and Hastings, puts up with a lot of annoying eccentricities from Lorna.   But I also see Annie's point of view in this, I have my fair share of outrageous and eccentric friends.  They really do bring a zest to life. 
Every time Person X calls I think, 'Oh boy, here we go.'  And I generally end up with my purse clutched to my chest sitting across a table from a notorious person in a dank basement thinking either, 'No one is going to believe this,' or 'How am I going to explain this?'  Every time Person Y calls  (left to our own devices, neither of us are into drinking and carousing) we end up somewhere we can remember getting to (like the desert?) and someone is missing a shoe.   And every time Person Z is in town I'm so worried that I'm going to be on the wrong side of a DEA investigation I find myself taking a lot of headache remedies and checking the bottom of my car for strange black boxes.  These are the people who bring out parts of my personality that lay dormant most of the time. (Thankfully.)  Or possibly I do the same thing to them.  Let's just blame it on our chemistry together.
The older I get the more I cling to these old friendships mainly because we have "history" and there is a lot of water under those bridges.  And I find it easier to recognize new friends, not all of which where we end up goading each other into a troubling situation. (Again, thankfully.)  But for Annie and Lorna, two people in a fictional world who became fast but enduring friends?  Book 3 The Rot is Deep left one of them (possibly) dead. Which leaves me with a big fat plot question to begin book 4 Red, White, and Scotch?  And that leads back to my original thoughts on the binding of sidekicks and enduring friendships and a lot of 'what if' questions.