Emotional pain is at the root of our tendency to withhold, and this causes pain to the people subjected to it.
No one deserves to be subjected to withholding. Feeling ignored, disrespected, or shut out, and to not know why, is a terrible feeling. The first thing to remember if this is happening to you is that you are not to blame. You are caught in someone else's pain pattern. This person does not know how to express feelings in a healthy way probably because this is what they learned when she or he was a child. The second helpful thing to remember is that the withholder is acting out of pain. They are stuck in a habitual mode of response that is self-defeating and alienating to the people they love. Remembering this will help you feel compassion for the person hurting you. However, if you have suffered too long with this pattern, you may need to get some space. Take some time to look at your own patterns and understand why you have taken part in this drama. If you are dealing with people in a family situation, you can step up to the plate to help break the chain of this behavior pattern.
If, on the other hand, it is you that tends to withhold, understand that this is a learned response and it can be unlearned. Find safe places to begin to express all that you've been holding back. Begin to make an effort to say what you're feeling and thinking. Give praise to someone you love. The more you do this, the healthier you and your relationships will become. What was learned over a course of a life cannot be changed overnight--remember, one day at a time.