How do we become bitter?

Genesis 27:41
Esau hated Jacob because he had stolen his blessing, and he said to himself, “My father will soon be dead and gone. Then I will kill Jacob.”

Esther 5:9
What a happy man Haman was as he left the banquet! But when he saw Mordecai sitting at the gate, not standing up or trembling nervously before him, he was furious.

We become bitter by letting anger and hatred control us.

How can I resolve my bitter feelings?

Matthew 7 v1-5 (Words of Jesus)
“Stop judging others, and you will not be judged. For others will treat you as you treat them. Whatever measure you use in judging others, it will be used to measure how you are judged. And why worry about a speck in your friend’s eye when you have a log in your own? How can you think of saying, ‘Let me help you get rid of that speck in your eye,’ when you can’t see past the log in your own eye? Hypocrite! First get rid of the log from your own eye; then perhaps you will see well enough to deal with the speck in your friend’s eye.

Ephesians 4:31-32
Get rid of all bitterness, rage, anger, harsh words, and slander, as well as all types of malicious behaviour. Instead, be kind to each other, tenderhearted, forgiving one another, just as God through Christ has forgiven you.

2 Corinthians 2:7
Now it is time to forgive him and comfort him. Otherwise he may become so discouraged that he won’t be able to recover.

We need to start forgiving and forgetting. We would do well to remember that God has forgiven us despite our continual sinful tendencies. There are times when simple forgiveness can relieve a lifetime of bitterness. Recovery from acute bitterness may be as complex as the reasons for the bitterness, but it may also be as simple as three spoken words: “I forgive you.”