Most of the time, the people you will come across do not want to cause any conflict, but sometimes, a person may unintentionally stir up a problem. While it may be tempting to lash back, the best thing to do is to assume good faith, and that the person had good intentions of their actions.
How to Assume Good Faith
Calm down if you feel frustrated. Most likely, nobody intended for any harm, so before you respond back to them, take a deep breath, count to ten, and see if you could possibly have made the same error. Consider how the person could have been easily trying to do something else. Maybe they are a little inexperienced, or maybe they made a mistake that they caught as soon as they did it. It's best to give them some space if they are a new editor.
Don't jump to conclusions. Something that seems obvious to one person may be a foreign concept to another. While you may feel the urge to scream at a person that erased all of the important information from a business seminar from a whiteboard, he or she could have been trying to help by cleaning off the whiteboard for others to use. A child whose best subject isn't math and only got a B on a math's test may have done all of their homework, studied for hours and paid attention in class. Trust each other's actions and don't automatically assume that they're wrong.
Realize that everyone makes mistakes from time to time. Mistakes are a way of life, and you won't see eye to eye with every person on the planet. There will be times when you think that one solution is better than another and so on. However take advantage of the opportunity to expand the article to have multiple methods so the article can cater to as many needs as possible. The world is full of diverse people with diverse opinions, and it's better to learn to accept that than to be stubborn when expressing your ideas.
Decide if you should step in with coaching the person. A person making the same mistake over and over may call for a friendly reminder, but nobody likes a person who calls them out on their every fault. Put yourself in their shoes. We were all beginners at some stage learning how to contribute. If someone was trying to help you fix a behavior, would you like it if they came up to you and barked at you about all your mistakes?
Learn from their mistakes. Prevent the same situation from arising again, chalk it up, move on, and smile.