I just ran Boston today, slower than my qualifier. Here's why:
My home marathon is flat and fast as is the terrain I train on, which allowed me to BQ with 15 min to spare. I PR'd there 6 weeks ago and did Boston today, for the first time. Having only 6 weeks to recover and run another marathon, let alone train my leg for hills, was a tall order.
Not knowing the course I paced super conservatively from the start. I didn't even look at my watch and ran by feel. I'm glad I did, because although I wasn't able to even come close to my PR, my fastest mile was my last and overall it was a great overall experience. I saw some people hauled off by ambulance-ATVs in the Newton Hills, and others moaning in agony clutching their quads doing the death-walk up Heartbreak Hill.
Although, I didn't equal or exceed my PR here, I now have a very attainable Boston-course PR to come back and break. At the same time, I was able to finish much stronger than most marathons I've run.