Often, the cause is more subtle and indirect, and many times not even our fault. For example, a child may feel responsible for his parents' divorce.
This is unwarranted guilt. But is it ever valid? Yes. Feeling guilt is our conscience at work. It is the conscience's way of letting us know not to do something again, or that something is harmful to society, which will in turn come back to us - not as a punishment, but as a cause and effect. It is not meant to become a debilitating burden.
What would be the point of continuous mental and emotional punishment for a momentary lapse of good judgment, or from lack of knowledge of the consequences of an action?
Let go of the misconception that only children are allowed to make mistakes and that the learning process ends in adulthood. By doing this, we can be more forgiving towards ourselves and others, and guilt can serve it's purpose: warning us when we do something inappropriate.
While doing this meditation, you may find you feel guilty about things you never considered. If so, this can be a starting point for finding the root of such guilt and the lesson it inspires.
Most of all, this is a meditation intended not to absolve us from a guilty conscience, but rather to help us find the cause of guilt, take the gifts and lessons our experiences carry, and get in touch with our humanity by bettering ourselves and, in turn, the world around us.
Prior to the meditation, record in your journal the issue you feel guilty about.