Know Your Limitations
Maybe this seems obvious, but just because you know that something isn't right, that doesn't mean that you know how to make it right. In other words, knowing that something is broken isn't the same thing as knowing how to fix it. If your car stopped working and you knew it had enough gas, how much time would you spend trying to fix it? There aren't too many things that I can fix on a car, so I personally wouldn't spend too much time on the problem; I'd call someone who can fix a car and let them work on it. It may be more expensive today, but in the long run it's more likely to be less expensive and much more effective assuming that you've found someone who knows what they're doing!
Similarly, if you see that someone is unhappy, even if you know the cause, you might not be able to do anything useful about it. Good intentions aren't enough, you need skill as well. If you try to help someone without knowing enough about how to do the job, it's likely that you'll make things worse.
This is especially true in your own relationships. There's a story of a woman, let's call her Jane, who never got along with her mother. Eventually Jane decided that she'd like to have peace between herself and her mother. So she arranged a meeting, which she went to with lots of hope. Shortly after they met, they were fighting again. When she related this story to a teacher, the teacher told her that basically nothing had changed between them, so the end result of a meeting between them was almost certain to be a fight. His advice was for Jane to develop her interpersonal skills more, develop a greater sense of compassion for her mother, and then approach the situation slowly, starting with letters and ending with a meeting. It probably took longer than Jane would have liked, but it did work. That's the way it is with most things, isn't it? I mean, to do them effectively always takes more time up front than to do them quickly, but doing them quickly often doesn't work.
Basically my point is, don't mess with other people's lives unless you know how to go about it. If today you recognize that something isn't right assuming it's not an emergency try to learn more about how to deal with the situation before trying to do anything about it. Because of the amount of time involved, you might not ever get to fix the problem, but if you do, you will have a much greater chance of success than if you just jump in and add to the confusion.