A Better Tomorrow
Impossible Toughness Saves
If the DC of a Toughness save is so high the character cannot possibly succeed, even with a 20 on the die roll, the Toughness save is still rolled to determine the effect (the amount the save misses the DC).
A natural roll of 20 means the character suffers only the minimal result of failing the save, regardless of the DC. Fate intervenes to spare the character from otherwise certain doom.