Before revision: Cotranslational folding is expected to occur when the folding speed  of the nascent chain is faster than the translation speed of the ribosome, but it is difficult to predict which proteins cotranslationally fold.
After revision: Cotranslational folding is expected to occur when the folding speed and stability of the nascent chain is faster than the translation speed of the ribosome, but it is difficult to predict which proteins cotranslationally fold.