Critical Result Skill Bonuses
From D&D Wiki
If you are playing with Critical Result Skill Bonuses, you can gain a +1 to your Ranks in any Skill through rolling a 1 or a 20 on a Skill Check. Simply roll a percentile every time you roll a 1 or a 20 (a critical fumble/hit). If the result is less then or equal to your Intelligence modifier, you gain a free rank in that skill. This free rank can even take you above your level maximum for that Skill.
This newfound knowledge or ability reflects wisdom gained from experience, either from realizing the cause of one's own mistakes or the reasons behind a grand success.