The Bible states that every human being who has ever lived has sinned, that is to do something, whether in thought, word, or deed, that contradicts God’s perfect and holy character (Genesis 8:21, 1 Kings 8:46, Ecclesiastes 7:20), and these are just the Tanakh (Tanach, Torah, Hebrew Bible, Old Testament) verses.
Adam and Eve when first created by God, were perfect. They fell into sin when they ate of the fruit of the tree that God had told them not to eat. Regardless of how big or little a deal this was, the reality of their action is that they they disobeyed and sinned against God.
In God’s eyes sin is sin. Whenever we do anything that violates God’s Word, that is sin, regardless of how big or small, serious or minor that sin may be in our opinion, or even in the opinion of our world culture.
Even more difficult to understand is that even when we do things that are “good”, without being saved (receiving salvation) they are coming from a body that is tainted (Isaiah 64:5 Tanakh [Isaiah 64:6 OT].) “And we all have become like one unclean, and like a discarded garment are all our righteous deeds, and we all have withered like a leaf, and our iniquities carry us away like the wind.”
It is like a dirty pitcher pouring out the water contained in it. There will be contaminants in the water because the pitcher is not perfectly clean. It is the same with us. We have inherited the spiritual DNA of our original ancestor, Adam. We are not clean. Spiritually we are dead, separated from God.