Karma is something which caused you a lot of pain in another life time, it is blocked, and it is something you are running away from with all your strength in this lifetime. You have a memory of that life in which it caused you so much pain. An unconscious memory, yet it is still a memory. And that memory prevents you from doing something similar in this lifetime.
And you may ask me: “If I cannot do it, why is it that I want to do it, why do I know that I have to go there?” And I will answer: Because this karma has to be unblocked within this lifetime. And if you come into this life to cleanse karma, until you have relived this memory again, accepted the pain, you will be unable to free that karmic energy and so you will be doing nothing worthwhile here.
In short: Identify the thing that you have most difficulty in doing, think about doing it. Let your fear take hold of your heart, open your heart, remove that density, cry if you feel the need to, but cleanse. And each time you think about it, it will hurt a little less. And every time you try to do it, you will get a little further. This is how one begins to cleanse karma. This is how one begins to give meaning to reincarnation.