Mistakes made dealing with the 2010 European debt crisis are coming home to roost in the current Greek drama, Harvard economist Ken Rogoff said Wednesday.
He said "the original sin" was to not write down debts across the board when the crisis first hit. "It would have cost a lot less," he told CNBC's "Squawk Box."
But international creditors did not want to do it then or now because of the precedent it would set for other debtor nations, such as Ireland, Italy, Spain and Portugal, the former IMF chief economist said.
"Once you do a massive writedown for Greece, they also need to turn to everyone else," he continued. "I think if it were just Greece it would have happened a long time ago."
The current problem with Greece, according to Rogoff, is "there's no way they're going to pay the debt."
Read MoreMarket ignoring Greece's Lehman moment: Strategist
On Wednesday, Greece asked its creditors for a third baliout to tide the debt-stricken country over for three-years. The Greek finance ministry has said a concrete reform proposal will be sent Thursday, ahead of Sunday's euro zone deadline for a deal.
"The only way to keep Greece in the euro zone is to give them a big haircut and give them banking support," Rogoff said. "It's hard to see how to do that when they're not sort of following the rules like other countries are."
He said the Greek government has been spending "far above" its means and "they haven't really been repaying yet."