Today's wanderings in the land of making myself a better developer led me back to Katrina Owen's 2016 RailsConf talk "Succession."

One thing in it struck me enough to capture in my commonplace book:  

"You want to encapsulate the concept that varies, not the concept that stays the same."

Thinking about that... essentially that you want to capture and put a nice border around the thing that is different – that's going to be more complicated.    And to keep finding the smallest difference and drawing it out – rather than finding the things that are similar and drawing them out.  

It seems like a big conceptual change in how one refactors - I think it's more subtle than it sounds – but I'm going to be trying to keep it in mind over the next while.