Who can say, “I am clean, pure”?

Proverbs 20:9
New King James Version (NKJV)

9 Who can say, “I have made my heart clean,
I am pure from my sin”?

Proverbs 20:11
New King James Version (NKJV)

11 Even a child is known by his deeds,
Whether what he does is pure and right.