How do we know that humans are totally depraved?

The doctrine of total depravity teaches that following the fall, every aspect of humanity is corrupted by sin, as seen in Romans 3:10-12. The inability to seek God or understand spiritual truths is highlighted in John 3:19-21, where it states that people loved darkness rather than light because their deeds were evil. This total depravity aligns with the understanding that without the work of the Holy Spirit, individuals cannot perceive, accept, or act according to God's truth. The fallen nature is so deep that individuals are not only sinful but are also blind to their sinfulness.