“Each heart knows its own bitterness, and no one else can share its joy.” No one can really really know what is going on emotionally inside another person. Only I have the window to my soul. There are always pieces of me that I hide—that only I know about.
But we can also talk about bitterness. Bitterness has its consequences. Physical consequences are chemical imbalances such as ulcerative colitis and hypertension, among others; loss of sleep and physical fatigues. Spiritual consequences can be an inability to love other people and therefore love God (1 Jn. 4.20-21), spiritual doubts, and becoming a stumbling block to others. Emotionally bitterness can cause depression. Bitterness can cause stress, resentment, and steal away our contentment. It can even affect our children and grandchildren (Dt. 5.9).
And we should also talk about joy. Joy is not as much a feeling of happiness as it is an understanding of God and “the way things work” that cause us to not be anxious about anything (Phil. 4.6), to look at life with the proper perspective and take rest in God alone (Mt. 11.28-30). It’s how we can rejoice in trials and suffering. It’s not because we’re happy about it, but because we understand how things work, and what God is doing (redeeming our pain, and making us holy). Joy is not the smile on our face, but wisdom in our hearts as we have been talking about in the book of Proverbs.