Believe you're going to change everything. Sort of.
You might not, but it can get you through the hard work. Just don't believe it too hard.
It's a conundrum: when dreaming up an action, and carrying it out, you may have to make yourself believe that this action is the one to really, finally, put an end to the injustice it's trying to highlight. But once you've done the action, it's important to remember that, well, it's just an action, one among many, and now you have to give it its chance to live or die at its own pace.
It's like setting off fireworks: once you've done your action of kindling the fuse, it's really best to stand back and let it take its course. The metaphor of course isn't great; in your case you, yourself, are part of the fireworks, and come in at the proper moment to send out your press release, answer questions from reporters (if you're one of the people cited), and possibly do damage control. But insofar as you can only steer the thing after it's launched, it's best to be ready to think of the next thing, and not get too attached to what just happened.
One symptom of over-attachment is a desire to make the action live longer by redoing it the next day, or extending it with new inflections just thought of on the spur of the moment—almost always an error.
Another is to fret too much about how the press release is put together. It's necessary to give whoever's sending out your press release the autonomy to do it without tons of meddling—even if things may be missed.
Another is worrying too much about getting credit; you should get credit, but also know that you are very likely to do another action again soon, and that it's the whole experience that's valuable, not the notch in your arrow.