Bitterness towards someone can be easy to fall into. Where they did not keep their word, betrayed you or whatever. Usually leaves you with hate and blame
but the truth is, hate and blame will not help you.
Yes it will make you feel better
but it wont help you toward your goal, the exam your trying to pass, obstacle your trying to overcome, or skill your trying to acquire.
No amount of blame and hate can help you toward your goal.
So if you step back and look at what bitterness is, its just a person alone, pouting about what a person did and with no positive effect.
so are you still going to be bitter?
or you can
Instead use that energy too propel you toward your goal, instead of getting upset about what he or she did. use that energy to use it towards something that will help.
Since small, little changes or adjustments make a huge difference.