Saddles are mysterious to me.

Last summer I went through a stretch where the saddle on my bike I ride for long distances felt terrible for the first 20 miles of every ride. Then it would settle in and feel great. Then after a few weeks it felt perfect again. I don't fully understand it, but I've assumed that something else is going on (subtly) that changes my position...maybe something else is sore and I'm sitting slightly differently.