Why is pride such a problem?
Pride was the first sin ever committed in the universe. The one who committed that grievous sin was Lucifer. He thought he was equal to God and wanted to be worshipped like He is worshipped (Isaiah 14.13-14). When God refused to share His glory with Lucifer (Isaiah 42.8) he rebelled and took one-third of the angels of heaven with him (Revelation 12.3-4).
Pride is often the root of most sins. People lie to protect themselves or harm others because they think they are too important to be caught or that others are less important than they are. Many sins are caused by pride: stealing, hurting others, coveting, causing dissension, etc.
If you have a problem with sin you most likely have a problem with pride. The only way to eliminate pride within you is to replace it with humility.
"Pride goes before destruction, and a haughty spirit before a fall" (Proverbs 16:18).