When I sit in quiet and in peace -- though perhaps not peace in my own heart -- I am strongly aware of the fact that pride is my worst sin. Pride in that I think I can do my tasks well on my own; pride in that I do not admit my mistakes; pride in that I hesitate to ask questions at the risk of looking like a fool; pride in my dealings with others, where I make assumptions about their lifestyles, and become satisfied with myself for not being like them. C.S. Lewis said that "a cold, self-righteous prig who goes regularly to church may be far nearer to hell than a prostitute".
I look at myself and I realize that I have wrapped myself up in a shell of ice. I have created such a safe comfort zone that any outside conflict that would threaten my sense of indifferent "happiness" is avoided by me at all costs. I will do anything to maintain that vague feeling of "all is well", and thus to hand on to the next person any uncomfortable responsibility.
I continue in this way because outside influences tell me that I am doing all right (such a mediocre term), and my pride clings to that label as the decisive judgment. When people are told how they are doing, and told often, they feel no incentive to find out for themselves. To a certain extent, I am reminded of Julia Flyte, a character in the book "Brideshead Revisited", who convinced herself that she really was happy and at peace -- though she was living in sin with Charles Ryder. But she broke down her walls at the honest words of her brother, telling her that his morals did not allow him to bring his fiance to Julia and Charles' house. Julia was, of course, talking about a different sort of sin, but I feel her words to be synonymous to my own thoughts:

'Living in sin, with sin, by sin, for sin, every hour, every day, year in, year out. Waking up with sin every morning, seeing the curtains drawn on sin, bathing it, dressing it, clipping diamonds to it, feeding it, showing it round, giving it a good time, putting it to sleep at night ... Christ dying with it, nailed hand and foot ... No way back; the gates are barred; all the saints and angels posted along the walls.'

Her words later in the book are also beautiful to me.

'I've always been bad. Probably I shall be bad again, punished again. But the worse I am, the more I need God. I can't shut myself out from His mercy.'

Pride may be the hardest fault to conquer. It may never be fully conquered in this life, for some of us. For me, I know this will be a life-long struggle. I will only be fooling myself if I think I can be better tomorrow, immediately. But I do know that any change that occurs only does so through God's great mercy.