Proverbs 15:13 shows inner joy or sorrow affecting the face — expanding on the heart's private bitterness and joy here.

Proverbs 18:14 describes a crushed spirit as unbearable — building on the inner bitterness known only to the heart.

1 Samuel 1:10 shows Hannah's bitter distress — a real-life example of the heart's private bitterness stated here.

In Job 6:2-4, Job describes his personal bitterness as heavier than sand—no one else can fully grasp its weight, matching the proverb's theme.

In Job 7:11, Job declares he will speak in the bitterness of his soul, directly echoing the inward bitterness of the heart.

In Job 10:1, Job again speaks of the bitterness of his soul, emphasizing his personal anguish known only to him.

In Mark 14:34, Jesus says 'My soul is very sorrowful,' an explicit confession of inward anguish like the heart's own bitterness.

In John 12:27, Jesus says 'Now is my soul troubled,' a direct expression of personal turmoil, echoing the proverb's inner bitterness.

1 Kings 8:38 describes each person knowing the affliction of his own heart—direct parallel to the heart knowing its own bitterness.

2 Chronicles 6:29 repeats the phrase 'knowing his own affliction and sorrow'—direct parallel to the heart's own bitterness and joy.

1 Corinthians 2:11 teaches only a person’s own spirit knows their thoughts — exactly parallels the heart’s private bitterness and joy.