The solution. Be honest, tell them whats up. Most of the time its because you really like someone and are just nervous about everything. Take your time and in no time you will be back.
Sometimes you will just need a minute or a couple of dates. If the girl judges you then you don't want to be with her anyways.
Very common in men with over active libido's as because they are constantly aroused, they can get side tracked. Especially if they really like a girl.
Usually is not a problem for those seeking a one night stand, but happens to those who have had enough of them to know they want something more.