To better something, he has to take that "condition" from another similar item. To improve a watch, he has to steal the condition from another watch. To become happy, you must steal the happiness from another. Equivalent exchange sort of deal! For people, it should last a couple of hours, for objects a day or so is fine!
ADDENDUM
To better something, he has to take that "condition" from another similar item. To improve a watch, he has to steal the condition from another watch. To become happy, you must steal the happiness from another. Equivalent exchange sort of deal! For people, it should last a couple of hours, for objects a day or so is fine!
Let me know if this works!