If you want to blame Summers, the key was that he allowed or wasn't able to stop the university from purging in 2005 the Harvard Management Company team that had provided their outsized earnings for so long. Although you can't necessarily blame him for making sure their inept replacements didn't squander money after he himself was purged in the following year. (E.g. the lost a billion dollars simply by not noticing one investment was going to hell and ending it.) And certainly not for the university pretending that after getting rid of that team they'd still be able to earn the same amount of money.