Nothing stops Greek government from defaulting. Just miss your next coupon payment, and viola. But once you default, you have to balance your budget, because n

Nothing stops Greek government from defaulting. Just miss your next coupon payment, and viola. But once you default, you have to balance your budget, because nobody will lend to you, and until 2017 Greece were running a deficit. Default would cause even more pain than so much hated austerity.