"Radical acceptance" means completely and totally accepting something from the depths of your soul, with your heart and your mind. You stop fighting reality. When you stop fighting, you suffer less. That means you don't feel hot anger in your stomach whenever you see the person who got the promotion you deserved, and you don't seethe with resentment when you see your best friend, who is now dating your ex-boyfriend. You accept what is, learn, and go forward.
Radical acceptance is easier to understand than it is to practice. There are many obstacles to giving up the suffering of resentments and anger toward others, toward God, or toward the world in general.
1. I don't want to let them off the hook. Holding on to your anger can seem like you are punishing the offending person, whoever did wrong to you. As long as you are angry, then they aren't getting away with whatever they did to harm you. Your anger serves as a marker, a memorial almost, of their actions. If you let go of your emotions and radically accept, then it can seem like it never happened. You don't want it to be that easy for the other person. When your feelings are deep and intense, you want the other person to understand the hurt they have caused. Plus, your resentment is pretty intense too and difficult to manage.
That sounds good. The problem is that it doesn't really work that way. When someone has treated you unfairly, he either knows it or doesn't. If he recognizes his actions were unkind, then your anger serves only to distract him from facing his own failings and guilt. If he doesn't recognize his unkindness (or worse), then your anger changes nothing. Your anger will not teach another person about compassion or kindness or respect for others.
Radical acceptance does not mean that you embrace the person who hurt you as if nothing happened. You go forward with knowledge that you didn't have before. You stand up for yourself with respect. The anger and resentment serve as messages to be more careful in the future, to stand up for yourself in effective ways, to strengthen your support system, and to use whatever knowledge you gained to be more effective in living your life. Holding on to the anger or resentment handcuffs you to the past and keeps you reliving a painful event. You continue to suffer, though the event is long since past.
The same information is true if you are angry with yourself. Forgive yourself and move on with what you have learned. Punishing yourself does not help you live more effectively.
2. Accepting means I agree; I will never agree. I think the problem is that the word "accept" often means approving of something or agreeing with someone, such as accepting a job offer means agreeing to take the job. Radical acceptance does not mean you are agreeing to a situation or action. It means you are acknowledging that the event happened and is real. Acceptance means not fighting reality. There are many ways to fight reality.
Your language is a clue that you are not accepting reality. You say something, for example, a wedding, shouldn't have happened, that you will never accept he married her, that you will hold it against him to his dying day, and that you will never acknowledge their relationship. The suffering is yours. The reality is that he did marry her. Your refusal to accept it doesn't change the facts and only holds on to emotional pain for you.
The same information is true if you are not accepting your own behaviors. The truth is that you did whatever you did. You don't have to approve or agree, but the facts are the facts.
3. I need to be angry to protect myself. Radical acceptance can seem very risky to emotionally sensitive people. Anger, withdrawal, and resentment can seem like armor to protect yourself. You may be seeking safety from the person who hurt you. Perhaps you forgive too easily and forget that someone behaves in certain ways, so you get hurt again.
The answer is not to protect yourself from possible future suffering by doing something that creates suffering in the present. In this case, find a different way to go forward, with wisdom, so you don't let the same scenario happen again and again. My guess is that attempting to use anger in that way works only for a short time anyway.
You may be using anger to protect yourself from more painful feelings, such as hurt, sadness, or emotional pain. As long as you stay angry, you don't feel as vulnerable. Feeling sad and hurt can make you feel quite vulnerable. In this case, anger is a secondary emotion, and you are blocking your primary emotions. As long as you block your primary emotions, you cannot heal.
Practicing radical acceptance can be very difficult, but the relief from suffering that results is worth the effort.