u/HTSike

Okay so I’m pretty familiar and understanding when it comes to priority with spells but how similar are activated abilities, for example my opponent has an ability that can pull something from his graveyard. Can I respond and remove the card allowing him to do so? If so does he still loose the mana or expenses he used to activate that ability (like if I used a counterspell when they attempt to cast something?) and will he get the thing from his graveyard still?