Our ego-minds are constructed to keep us surviving no matter what. Our happiness is not a consideration—only our survival, which includes avoiding pain and seeking pleasure. So if we let this automatic entity keep running our lives it will also ruin our lives.
That is why we must be aware of how the whole automatic and repetitious activity of the mind works. Once we truly see it, then we are in a position to tame it. Taming it means letting it run in the background but not paying attention to its every agitation. It means being the boss of our mind instead of it being the boss of us.
The mind, which is not eternal and is subject to failure an disease, is in the foreground, scanning our physical reality like radar. The Spirit, which is eternal, is in the background, observing it all without getting caught up in the ups and downs. It is purely at rest. When you understand how the mind works, with its ceaseless chatter, then you will be able to see its patterns and you will be able to rest in the Spirit.