Abraham Maslow noted that certain needs take preceedence over others. That if, for example, if you're thristy and someone has you in a choke hold, the need for oxygen will take preceedence over the need for water. And thus a 'hierarchy of needs' emerges, with higher needs not being taken into consideration, or totally fulfilled, until lower needs are met.

At the bottom of the table we have phisiological needs - the need for food, water, shelter, rest, sleep, activity... the physical things we need to survive.

Above this are our needs for safety and security. Of course, just like the choking guy doesn't care about water, people who have no food to eat don't really care about safety and security. That said, once you've got that you obviously want to make sure that's secure.

Third, we have love and belonging needs. This covers things like relationships, friendships, sex and a sense of belonging in the wider community or society.

Fourth we have self esteem needs. We can divide this into two halves, the lower a set of self esteem needs based on level 4 morality.

The higher subsection of these is based more on Kohlberg's level 5 morality, and includes confidence, competence, achievement, mastery, independence, and freedom.

Once all these needs are fulfilled to a reasonable extent, an individual can self-actualize. Of course, this opens up a whole nother set of needs to fulfill.

Furthermore, a problem in the lower needs manifests itself in the higher needs. So if you're having relationship problems, your self esteem suffers. You often hear of people who feel insecure having problems with relationships and their self esteem. Similarly, the higher up you go the table the harder it is to fill the need: for instance, if you're hungry, the answer is simple: eat! But if the problem is, say, with self esteem, it could be a manifestation of the needs on any of the needs below it.

We can also see this shown on a society wide basis. How often have you sat back and seen a war in a foreign country and thought "How can people do that to each other?".  The answer is simple, hungry people kill for food, thirsty people kill for water, and a humiliated nation fights for pride,a nd its charismatic leader.

My Personal Gripe
My personal gripe is with a lot of right wingers who think that, by cutting people's ability to fill their D-needs, somehow crime will go down. Morons!