An activity action has two possible places for Casus_Belli_Success: once the action successfully is started and once the action is completed.
"Pillage" currently triggers the Casus_Belli_Success effect when successfully starting the "Pillage" action. The Casus_Belli_Complete effect is triggered once the activity is done.
This may be counter intuitive. Argue here (or file a bug report or feature request) if you expect the Casus_Belli_Success to be evaluated on activity completion and another effect - like Casus_Belli_Successful_Beginning - to be evaluated at successful "Pillage" start.
Casus Belli effect name for activity actions
Re: Casus Belli effect name for activity actions
Another, related, question is what you expect Casus_Belli_Complete to do for instant actions. (If changed to Casus_Belli_Successful_Beginning the question becomes what you expect Casus_Belli_Successful_Beginning to do for instant actions.
Re: Casus Belli effect name for activity actions
I think all is right, we consider the action to be performed ijn the moment of switching to the activity. When Burgundian soldiers have just started breaking a road in Moravian territory, it's already a casus belli. Maybe diplomats are able to turn it into a joke, but only until the road is actually broken (maybe otherwise we need a confirmation message before setting the Pillage activity?).