Why do I want to study corruption?

There are many "?" that shine like stars in my sky:
? : why do I exist like this and not that?
? : why is there love or hatred?
? : why are people selfish?
? : why is there war?
? : why do I ask?
.......
But, at this moment, i most urgently want to know:
? : why is there so much corruption?
What does it mean if a country is featured with widespread corruption? What does it mean if one or two government official is over millions units of money corrupted? What does it mean if one needs to be corrupted besides monetary motivation? What happened after a country is seriously corrupted for a long time? What is the worst consequence of corruption? Who benefits most from corruption and who the least?