Most people think at least some of the wrongness of an action is the harm it causes. There are other potential ways of wronging someone, such as using a person as a means rather than an end, but while that factor is controversial, very few people doubt that causing harm has no moral role. Many people also think it's plausible to distinguish between the goodness or badness of the act itself, on the one hand, and the goodness or badness of the person's decision to act, on the other.
Although we usually think it's the harm itself that matters, there are reasons to think that harm can't be the whole story. If I put you in a dangerous situation, it's strange to say that I have wronged you only if you end up being harmed. If I'm drunk and I force you to ride with me as I drive home from the bar, it's clear that I have acted immorally. I ought to be censured (and worse) for my carelessness.
Importantly, we can think this whether or not I crash the car. Suppose I get us home safely in case A, but in case B I crash and we are both seriously hurt. Case B involves more wrongness because more harm is caused, but I acted equally poorly in both cases (because I acted the same). The reason is that risk matters in addition to outcome.
Even consequentialists—those who think only consequences matter in determining morality—can distinguish how well a person acts and the goodness of the outcome of his act. They don't need to, that is, some consequentialists reject this move and maintain that all that matters is the outcome. But that has strange results, one of them being that in my drunk driving example I act immorally only in the case where I crash, even though I perform the same action in both cases.
Once one starts thinking about ethics, examples pop up in real life all the time. Recently I was given the opportunity to participate in a research study on omega-3 supplementation for athletes that a PhD candidate in the nutritional sciences department is doing. I run a lot, so the benefit for me is that I get free aerobic threshold testing, which usually costs $150. Participants are given either a placebo or a supplement made of seal oil, so there's a chance that I'll be eating seal parts, which (we might suppose) is unethical.
Of course, it's just a risk. I might be in the placebo group and will therefore cause no quarrel with my pinniped brethren, and will get the benefit of participating in the study. So it turns out it matters if there's a distinction between how we act and the consequences of our actions. In both cases I have some chance of acting unethically if I'm placed in the wrong group, which means that by participating in the first place I'm introducing that risk, so perhaps I ought not to participate. But if the distinction doesn't exist then there's some chance that I'll cause no harm, and because of the benefits of participation the case can be made for participation. To put it another way, perhaps the risk is worthwhile.
The next time you're given the opportunity to participate in a study on omega-3 supplementation you'll be glad you read this article.