Besides having a terrifying past experience, there can be some other ways too by which someone can develop this fear overtime.

One of the triggering points could be the news coverage of robberies and thefts that can contribute to this fear.

Although, it is said that the person's own experience can make things worse but it is also believed that observing other people's experiences and behaviours can also contribute to the formation of these fears.

If you see news stories on robberies, it may seem that these events are more common and therefore more likely to happen to you.

So reasons could be many as it depends on person to person and how they get influenced by the things from their surroundings.