Critical Success, Critical Fail

When rolling for an attack, a natural 20 is a critical success and automatically succeeds, and a natural 1 is a critical fail and automatically fails.
However, when it comes to skill checks and saving throws, these react a bit differently. On a natural 20 for a skill check or saving throw, double the modifier used in that skill (eg if you are rolling athletics, double your strength modifier). On a natural 1 for a skill check or saving throw, subtract the modifier used in that skill from the total amount.
This allows for some risk and reward in out-of-combat scenarios without the complete binary of automatically succeeding or failing.