What Is Sin?
Sin is when you make the wrong choices instead of following God's instructions. It separates you from His presence, love, and purpose for your life. When the first man and woman sinned, it caused each and everyone to be born with a sin nature. Sin separated every person from God.
You may be thinking, since you are a good person that would be enough to make you okay. Just being a good person is not going to erase sin and the sin nature.