Downward social comparisons can be a means of self-defense. People who have low self-esteem tend to look for other people who think they are somehow worse off than them to feel better, on the contrary. Over time, this is counterproductive, since that sense of worth is dwarfed when that person comes into contact with someone who they perceive is doing better than them. For the time being, that downward social comparison may seem to be resolving a sense of inferiority (well, at least I'm not as bad as so and so), but it's actually reinforcing the inferiority complex.
