Bonjour,
Quand tu décides d'activer une capacité (ou de jouer un sort), tu la met dans la pile
avant de choisir et les cibles (et autres choix) et de payer les coûts. Donc le sage n'est pas encore sacrifié que sa capacité activée est déjà en pile.
602.2a The player announces that he or she is activating the ability. If an activated ability is being activated from a hidden zone, the card that has that ability is revealed. That ability is created on the stack as an object that's not a card. It becomes the topmost object on the stack. It has the text of the ability that created it, and no other characteristics. Its controller is the player who activated the ability. The ability remains on the stack until it's countered, it resolves, or an effect moves it elsewhere.
602.2b The remainder of the process for activating an ability is identical to the process for casting a spell listed in rules 601.2b–h. Those rules apply to activating an ability just as they apply to casting a spell. An activated ability's analog to a spell's mana cost (as referenced in rule 601.2e) is its activation cost.
Une fois l'objet sur la pile, on applique dans l'ordre les étapes suivantes (je passe la plupart pour laisser ce qui concerne le problème soulevé ici) :
601.2g The player pays the total cost in any order. Partial payments are not allowed. Unpayable costs can't be paid.
601.2h Once the steps described in 601.2a–g are completed, the spell becomes cast. Any abilities that trigger when a spell is cast or put onto the stack trigger at this time. If the spell's controller had priority before casting it, he or she gets priority.