At certain times in our lives, difficult experiences happen. Some of those hard times felt overwhelming to us, whether because we weren't prepared to handle them (like when we were children), we were just not at our best at the time, or because the thing was really severe.
Because we felt overwhelmed when the difficult experience happened, our brain was "flooded" and could not do a good job of making and storing a memory that explained exactly what happened and why. Instead, all the information that went along with that hard experience – the thoughts, feelings, and body reactions - were stored in an unresolved memory.
The problem with an unresolved memory is that it is not stored correctly. All the hard parts of what happened are all mixed up, so our minds try but are not able to feel settled. When new things happen to us that feel similar to the unresolved material, they can trigger all that old confusion. When this happens, old thoughts, feelings, and body reactions rise up again. We feel now and react now as we did back then, while the difficult experience was happening.
EMDR is a healing journey. With EMDR, we search out the unresolved memories that are tied to your current symptoms or discomfort. Then one by one, we revisit them and have another chance to understand them and resolve them. This time in a way that we are prepared, and it is not overwhelming. After each memory is resolved, any new experiences that happen now will not cause that old stuff to come back up from the past. So, once we are done with EMDR, any uncomfortable feelings, negative thoughts about yourself, and even unwanted responses will probably get much better. You may even discover that more good things are true about you than you realized before. And the good news is that this change can happen better, meaning faster and more permanently, than if we talk about it.
You can think about it like this: A man was walking along a riverbank. As he was walking, he noticed people in the water who were drowning, so he began to reach in to save them. He kept saving people one after another until one day, he got up and left. When he was asked, "Where are you going? Who will save all these drowning people?" the man replied, "I am going to see who is throwing them off the bridge." (From The EMDR Revolution by Tal Croitoru)
So with EMDR, instead of providing tools to deal with your problem, we will resolve the issue - the unresolved memories. As each memory is resolved, the unwanted emotions, negative beliefs, and symptoms that go along with that memory often fade away.