Interesting theory i read about in Malcolm Gladwell's book "The Tipping Point":
The broken windows theory:
Consider a building with a few broken windows. If the windows are not repaired, the tendency is for vandals to break a few more windows. Eventually, they may even break into the building, and if it's unoccupied, perhaps become squatters or light fires inside. Or consider a sidewalk. Some litter accumulates. Soon, more litter accumulates. Eventually, people even start leaving bags of trash from take-out restaurants there or breaking into cars.
The article received a great deal of attention and was very widely cited. A 1996 criminology and urban sociology book, Fixing Broken Windows: Restoring Order and Reducing Crime in Our Communities by George L. Kelling and a co-author Catharine Coles, is based on the article but develops the argument in greater detail. It discusses the theory in relation to crime and strategies to contain or eliminate crime from urban neighborhoods.
A successful strategy for preventing vandalism, say the book's authors, is to fix the problems when they are small. Repair the broken windows within a short time, say, a day or a week, and the tendency is that vandals are much less likely to break more windows or do further damage. Clean up the sidewalk every day, and the tendency is for litter not to accumulate (or for the rate of littering to be much less). Problems do not escalate and thus respectable residents do not flee a neighborhood.
The theory thus makes two major claims: that further petty crime and low-level anti-social behavior will be deterred, and that major crime will, as a result, be prevented. Criticism of the theory has tended to focus only on the latter claim.
A major factor in determining individual behavior is social norms,
internalized rules about the appropriate way to act in a certain
situation. Humans constantly monitor other people and their
environment in order to determine what the correct norms are for the
given situation. They also monitor others to make sure that the others
act in an acceptable way. In other words, people do as others do and
the group makes sure that the rules are followed. However, when there
are no people around, as is often the case in an anonymous, urban
environment, the monitoring of or by others does not work. In such an
environment, criminals are much more likely to get away with
robberies, thefts, and vandalism. When there are few or no other
people around, individuals are forced to look for other clues—called
signals—as to what the social norms allow them to do and how great is
the risk of getting caught violating those norms. An ordered and clean
environment sends the signal that this is a place which is monitored
and people here conform to the common norms of non-criminal behavior;
a disordered environment which is littered, vandalized, and not
maintained sends the opposite signal: this is a place where people do
as they please and get away with it without being detected. Therefore,
as people tend to act the way they think others act, they are more
likely to act "disorderly" in the disordered environment.