Have you ever thought of your mind as being like the boot of your car?
You must have been told from time to time to clear out the boot of your car, because the weight you carry around in there costs you money in fuel that you burn to no purpose. I don’t mean the weight of the atlas, or the car-jack, or the spare tyre (which after all, you might need), but: the half of a pair of trainers, the discarded wrapping, the stuff you were taking to the dump but got distracted by something else.
Now think about your mind. What are you carrying around that you don’t need? Not factual memory: that doesn’t weight much, no more that a note in the atlas “I was in ‘Somewhere-or-another’ in June 2012”; or the positive memories, which are more like fuel than dead-weight; but the negative emotions.