Ah, the million-dollar question. Because the easiest way to shape the outcome at the end is to frame the purpose at the beginning, we work with clients to create mutually agreed-upon goals for what successful results need to look like, and then we are accountable to that.
The speed to results is often dependent on the marketing tactic and the goal of the tactic. For instance, if your goal is to grow brand awareness, that’s not something that happens overnight. Some marketing channels produce results immediately, whereas others take time to build momentum (see above about no silver bullets.)