Indeed, bitterness is a common problem that all of us have from time to time in our life. But many of us are not so aware of our bitterness as we should. Bitter feelings can go underground. They often don't display themselves in active forms such as hitting, pinching, throwing things or slamming doors. They take more subtle forms like silence, irritation, resentment and hatred.
Bitterness is worse than disappointment.
It can destroy any possibility of human relationships to continue. I remembered when I had been deeply hurt by the lady, much of time I was bitter with myself. I had expectations and demands for myself that I couldn't meet. And I became angry with friends. I've done things by myself all my life and I will continue to go on alone.