No doubt there have been times when you have caused harm to yourself or another - and you want badly to be able to forgive yourself. To alleviate the pain of the experience and transform it into a healing situation, you might try the following:
Don't fixate on berating yourself. Manage your thoughts of the situation. Don't let it consume your every waking hour. Be very careful not to label yourself. You're not "worthless", "no-good" or helpless. You are someone who made a mistake and are seeking to resolve it.
Guilt, like anger, sounds negative but has a positive purpose. When feelings of guilt arise, you are being made aware of a situation in which you are violating an internal standard. That's the positive purpose of guilt. Once you are aware, you take the corrective action. The corrective action helps you maintain integrity with yourself.