How do we know that all have sinned according to the Bible?

Romans 3:10-12 states, 'There is no one righteous, not even one; there is no one who understands; there is no one who seeks God. All have turned away, they have together become worthless; there is no one who does good, not even one.' This foundational truth underscores the Reformed understanding of total depravity — that all humanity is steeped in sin and incapable of achieving righteousness apart from divine intervention. The examples of individuals like Nicodemus and the Samaritan woman illustrate this principle: both are seen as flawed yet ultimately redeemed, revealing God’s mercy and grace in salvation needed for all, irrespective of their backgrounds or perceived righteousness.