The tendency to over-react when things go right or wrong brings suffering to ourselves and others involved with us. Thus our minds need training, so that we may find balance and stability whatever the outer circumstances. It is like training a horse that is frightened by the sound of fire. By gradually acquainting the horse with the noise of fire, he will no longer be surprised by it and will cease to panic when he hears it. Similarly, if in meditation exercises we confront anger and pain again and again, over a period of time, we will be able to face and deal with them in life.So, if distressing thoughts come up from time to time in meditation, that's actually what is supposed to happen!