This article introduces the concept of effectivity, which is the power to be effective or to achieve a certain effect to accomplish one's goals, in this case, desired school or life achievement. Giftedness would be better defined and developed in terms of effectivity than in terms of various concepts of ability. The concept of effectivity hinges on the idea that what determines, or what influences achievement, includes cognitive ability, but only as a small part of the total picture. Gifted "underachievement" as well as "overachievement" disappear when one understands giftedness in terms of effectivity.