That they lack money? All people have a variety of differences regardless of their lot in life. There are many "poor" people who are quite happy and live peaceful lives and have a great attitude about making due with what they have. There are others who have problems like addictions who have kind of made a hard life through bad choices, then others just hit an unexpected hard turn - layoffs, bad economy, businesses closing down. The same can be said for "rich" people - some of them are not happy despite having monetary wealth and they never have "enough". Others are very kind, hard working, generous etc. Some are born into wealth and never know the value of hard work etc.
Aside from not having money, I don't really see how there would be an across the board commonality among the poor - nor the rich for that matter? Everyone is different.