I take it you mean long distance relationships. Well I've been in one and I'm currently about to be in another one so I know it's very possible for long distance relationships to last, but it depends on the attitude of the two people involved in the relationship.
If both parties are actually willing to put in the effort to make it work then I'm pretty sure it can work, but if one person doubts that possibility even for a second then that's a recipe for disaster right there.
The most important thing is their communication, if the two people involved can maintain steady communication between each other then they shouldn't really have much of a problem. Granted long distance relationships are lacking in terms of physical contact, I've found that people who are far away from each other tend to communicate more than people who live close to each other. This is probably because talking with each other is all they have, without it then they're just friends who live in different parts of a country or the world.
Distance can be a good thing too, it can help you appreciate what it means to have the person you love beside you, and when you eventually make your relationship a normal one, you'll cherish it far more than people who've never experienced a long distance relationship.