Stonarch Pearl by Bob Greyvenstein
Spell Focus of Potential first appeared in the 5e Campaign Setting Adventurer's Agency.
Spell Focus of Potential
Wondrous item, uncommon (requires attunement by a spellcaster)
While holding this item, whenever you make a spell attack that misses, the focus begins to glow with potential energy. Whenever you miss a spell attack, add +1 to the next spell attack roll. This effect stacks for each missed attack (e.g. if you miss 3 times in a row, add +3 to the fourth roll). On a successful hit, all stacked charges are expended, resetting the effect to 0, and the glow dissipates.