I don't remember where I first heard about Boston 2 Big Sur; it just seems like one of those things that's sort of been in the water since I started running distance races ten or so years ago. I'm sure I first read about it on someone else's blog back in the day, or one of my very earliest Bay Area running buddies mentioned it in passing. Who knows. But for about as long as I've wanted to try to qualify for & run Boston, I've always known that if I did, I would try to complete the Boston 2 Big Sur Challenge as well.
Part of this has to do with wanting to run Big Sur, but not wanting to devote an entire training cycle to it since it's pretty much guaranteed not to be a fast race. So Boston 2 Big Sur kind of let me do a two-for-one: Train for and run a "for-serious" marathon (Boston), then run another casually while I'm still in shape to finish the distance reasonably well.
There was also the issue of getting in; the race is popular enough that there's a lottery, so you can't just assume you'll be able to run it whenever you want. (See this post for more details about the Big Sur Lottery.) Boston 2 Big Sur was the closest I'd ever come to being guaranteed a spot.
Of course, I'd never tried to run two marathons just 13 days apart, let alone running one of the toughest road marathons around just days after running what is on its own not necessarily the easiest marathon around. When I first started running marathons, I never would have dreamed of attempting such a thing, but October 2017 rolled around and I was feeling a bit nervy, so I figured, "Ehhhhh, what the heck? It's not a challenge if you're sure you can do it!"
(At least 2018 was one of the 13-day gap years; some years the two are only 6 days apart & I'm not 100% sure I'm *quite* that crazy.)
When I was first thinking about doing Boston 2 Big Sur, I had a lot of questions. I'm grateful for everyone on the internet who wrote race reports and shared their experience, so I thought I'd pay it forward & add to the collective bank of information that's out there. Obviously these are all just my personal opinions, and they're extremely colored by my experiences & background, so, as always, YMMV.