When someone is described as "high maintenance" I think most people instantly think it means they are picky, difficult or perhaps, if it's a woman, someone who has a lot of financial upkeep.  My definition of a High Maintenance Person is someone who relies on outside influences to obtain any sense of joy in their lives.  I think everything else stems from that.

If you are a self fulfilled person, outside influences such as material goods or praise from others is just icing.  You find joy from within.  Sure, outside influences can improve a good mood or amp up a bad mood, but at the end of the day, you are okay with yourself.  A high maintenance person isn't.

I have high maintenance people in my life and I think I feel the need to have some of them in my life.  I like being needed even though I might complain about it from time to time.  I enjoy feeling like I made someone happy.

Some high maintenance people can suck the life right out of you though.  You have to learn to not give in to your desire to try to please those types since no matter what you do, they won't be happy.  Some people have expectations that just can't be met by reality.

High maintenance doesn't necessarily mean they require material things.  It might mean that they require attention in the manner they expect at a rate that they expect or they won't be happy.  They are difficult to "deal with" from a low maintenance person's perspective because they don't let things slide like a low maintenance person would.  Outside influences seem to have more of an affect on the high maintenance person.

At this point in my life I wonder if a high maintenance person can learn to become lower maintenance.  I tend to think they can because I think it was life experience rather than predisposition that made them high maintenance to begin with.  I think I am pretty low maintenance though so it is hard for me to relate to the higher maintenance mind set.