Oftentimes, you may go into an apology feeling hesitant or resentful. If you feel something wasn't your fault, you may think an apology is unnecessary. However, if you made a mistake that hurt your mom, an apology is important. You need to acknowledge your part in hurting another person. Do not blame others for your actions.
You may feel the mistake was not 100% your doing. This is probably true. There are few situations in life where the blame completely falls on a single individual. External factors can easily influence a decision and can contribute to a mistake. An apology, however, is not about who or what is to blame. An apology is about taking your responsibility, however small, for your actions. Even if your mistake was mostly caused by other people or a situation, it hurt your mother. For example, you were talked into blowing off your mom's birthday party by your brother. While it was your brother's idea, you still blew off the party. You need to take responsibility for that.