There are two worlds you could live in – mentally speaking – utopia or the real world.
In Utopia there is no pain. Pleasure is permanent. Everything is just perfect.
Or you can live – mentally speaking – in the real world. In the real world there is both pleasure and pain. Everything is impermanent. It is not perfect.
It seems obvious to choose Utopia – who would not? However, there is one small problem with Utopia – it does not exist. In practice you anyway live in the real world. So it appears to us in our mental Utopia that nothing works right. Not only is there pain, but there is also anger since pain should not exist in utopia. Even if there is pleasure, the pleasure passes, leaving us with anger and anxiety. We have lost control. Things are not working right. Utopia turns out to be hell.
If you live – mentally speaking – in the real world, by recognizing there is no other world, there is, admittedly, pain. But no anger. Even if pleasure passes there is no anger. Nothing whatever is construed as a problem. This is the best possible of all worlds. It is the only real world.