Why people become so arrogant ?

Today i had to accompany somebody to a meeting with an arrogant fool. Fool's behaviour was so much full of arrogance that the whole place seemed to be a stinking gutter. I can't figure out that what makes such mortals to behave like they are holding powers of life and death over somebody. My philosophy in life has been that the biggest service a person can do is to help other people as much as he can. And if it doesn't involve any disadvantage to you than what's the problem man! I can't understand the logic behind refusing to help in such a scenario. It is a godsend oppurtunity that a person is able to help others. People do not become great by occupying high posts they become great when their deeds are great. It is a foolhardiness to think that one has to show off the powers he weilds. The moment somebody bangs his fists on the table and yells " I am the boss here", he ceases to be actually.