A roll-up summary calculates a parent value from related detail records. Count counts qualifying details; sum adds a numeric field; minimum and maximum find boundaries. The relationship and filter decide which records contribute. An amount from an unrelated account must never enter the total.
Separate a received gift from a pledge before adding donations. Both are valid records, but they don't represent the same financial event. An empty set can produce a zero count or sum, while a minimum or maximum may be unavailable. A formula field on the child doesn't automatically make every relationship eligible for a native roll-up. This simulator evaluates the supported master-detail relationship directly and checks an unrelated parent as well as the populated one.