Oh, great. Someone let the Monster in.
Just to state for the record: I've never met an endorphin. NEVER. I don't care who says what, I think y'all are making up the whole endorphin nonsense to justify your clearly addict-based passions for stuff like running and biking.
No, I don't "understand", either. I'll never understand. I spent three years running 30 miles a week, and other than a smug self-back-patting on a regular basis for having stuck with it (not an easy thing for me) I got nothing out of it. I wasn't even all that thin. I think I ate more, because of all that running. I'm sure my heart was heathier, I get all that, but MAN was that boring WORK.
I can't remember getting any deep thinking done, either. All I can remember thinking is something like "50 minutes to go! You can do it! The first 3 miles are the hardest! Jeez, I hate that itchy spot between my shoulder blades when I start to sweat! My underwear are riding up, is anyone looking, can I tug them down? 45 minutes to go! STILL? Only five minutes into it? Who runs in Florida, anyway? This is unbearably hot! Did my watch stop? Is the sweat killing my watch? Dear God, make that 45 minutes go by FAST!".
I did it because it was a personal challenge to do it, because I felt like if I kept with it long enough I would somehow magically meet that first endorphin (No! Never DID!), and because it was Good For Me. Like flossing my teeth and getting to bed on time is good for me. Like that.
Flossing isn't fun, either. No endorphins. It has exactly the same effect on my fun-o-meter as running. Zip.
Now horseback riding, that's a different thing altogether. For, you know, ME.
"What do you fear, lady?" Aragorn asked.
"A cage," Éowyn said. "To stay behind bars, until use and old age accept them, and all chance of doing great deeds is gone beyond recall or desire.”
― J.R.R. Tolkien, The Return of the King