These can be very different reasons. This will certainly differ from person to person. What is normal for one person may already be a sign that more than normal gambling is going on for another. If you enter an addiction phase, you should try to get out of it as quickly as possible. Write down the symptons.
I don't think it would be very much possible for the person to get out of the addiction after getting into it without realizing it.
Most of the people who get into the addiction to gambling always chase down their losses till losing it all and repeating the same cycle again and again.
Useless someone close to watch their habits they will not be able to get out of it.