Assuming good faith is a fundamental principle on any wiki. As anyone is allowed to edit, it follows that we assume that most people who work on the project are trying to help it, not hurt it. If this were not true, a project would be doomed from the beginning.
So, when you can reasonably assume that something is a well-intentioned error, correct it without just reverting it or labeling it as vandalism. When you disagree with someone, remember that they probably believe that they are helping the project. Consider using talk pages to explain yourself, and give others the opportunity to do the same. This can avoid misunderstandings and prevent problems from escalating. Especially, remember to be patient with newcomers since they will be unfamiliar with the wiki's culture and rules.
A newcomer's behavior probably seems appropriate to him or her and a problem usually indicates unawareness or misunderstanding of the wiki's culture. It is not uncommon for a newcomer to believe that an unfamiliar policy should be changed to match their experience elsewhere. Similarly, many newcomers bring with them experience or expertise for which they expect immediate respect. Behaviors arising from these perspectives are not necessarily malicious.
Assuming good faith is about intentions, not actions. Well-meaning people make mistakes, and you should correct them when they do. What you should not do is act like their mistake was deliberate. Correct, but don't scold. There will be people you disagree with. Even if they're wrong, that doesn't mean they're trying to wreck the project. There will be some people you find hard to work with. That doesn't mean they're trying to wreck the project either; it means they annoy you. It is never necessary that we attribute an editor's actions to bad faith, even if bad faith seems obvious, as all our countermeasures (i.e. reverting, blocking) can be performed on the basis of behavior rather than intent.
Of course, there's a difference between assuming good faith and ignoring bad actions. If you expect people to assume good faith from you, make sure you demonstrate it. Don't put the burden on others. Yelling "Assume Good Faith" at people does not excuse you from explaining your actions, and making a habit of it will convince people that you're acting in bad faith.
When edit wars get hot, it is easy to forget to assume good faith.
Assuming bad faith
This is what happens when you assume bad faith:
- Personal attacks: Once you've made a personal attack, the target will probably assume bad faith. The edit war will get even uglier. People, like elephants, rarely forget.
- Losing sight of neutrality. The ideal is to make articles acceptable to everyone. Every revert (rather than change) of a biased edit is a defeat for neutrality, no matter how outrageous the edit was. Consider figuring out why the other person felt the article was biased. Then, if possible, try to integrate their point, but in terms you consider neutral. If each side practices this they will eventually meet at a neutral point of view — or a rough semblance of it.
Correcting someone's error (even if you think it was deliberate) is better than accusing him or her of lying because the person is likely to take it in a good-natured fashion. Correcting a newly added sentence that you know to be wrong is also much better than simply deleting it.