You can concentrate even in the direst circumstances, and know how to retain your magic even when it would otherwise be wasted.
Benefit: Whenever you fail a concentration check while casting defensively and would normally lose a prepared spell or spell slot, you may attempt a Will save (DC = 15 + spell level) to retain the spell as though you had not attempted to cast it. The failed concentration check still results in the spell’s failure, even if the spell is retained.
Special: To gain the benefits of this feat, you must meet the prerequisite that matches the ability score you use to determine your save DCs, bonus spells per day, and ability to cast spells of a given level. If you gain spells from multiple classes, you must meet the prerequisite ability score for each class to gain the benefits of this feat when casting spells from that class’s spell list.