four noble truths

Now this, monks, is the noble truth of suffering: Birth is suffering, aging is suffering, death is suffering; sorrow, lamentation, pain, distress, and despair are suffering; association with the unbeloved is suffering, separation from the loved is suffering, not getting what is wanted is suffering. In short, the five clinging-aggregates are suffering.

And this, monks, is the noble truth of the origination of suffering: the craving that makes for further becoming — accompanied by passion and delight, relishing now here and now there — that is, craving for sensual pleasure, craving for becoming, craving for non-becoming.

And this, monks, is the noble truth of the cessation of suffering: the remainderless fading and cessation, renunciation, relinquishment, release, and letting go of that very craving.

And this, monks, is the noble truth of the way of practice leading to the cessation of suffering: precisely this Noble Eightfold Path — right view, right intention, right speech, right action, right livelihood, right effort, right mindfulness, right concentration.

wisdom of non-attachment

For what purpose, friends, is the spiritual life lived under the ascetic Gotama [the Buddha]?
It is, friends, for the fading away of lust [clinging] that the holy life is lived...
Excerpt from SN 45:41-1

I added clinging to the passage above because when we read lust we usually think of lust of a sexual nature. But lust or clinging (attachment or grasping) refers here to a more general wanting, any effort to escape the flow of our experience of the present moment.

The result of effort away from what is true in the moment, whether we do it through grasping, avoiding, or ignoring, is a cause of suffering. Lust is the root of hostilities and violence. Choosing openness to the moment is the most important thing we can do to end suffering in our lives and open to happiness.

Dealing immediatly with these automatic responses is not the same as actions we might want to take. Skillful actions can only arise out of awareness and acceptance of our experience as it is. This is what is true in the moment. It is then skillful to take action when circumstances require it. This is Wisdom.

why experience pain?

I declare, monks [dhammafarers], that actions (kamma) willed, performed and accumulated, will not become extinct as long as their results have not been experienced, be it in this life, in the next life or in future lives. And as long as these results of actions willed, performed and accumulated, have not been experienced, there will be no end to suffering.
-words of Gautama Buddha

Parallel saying in contemporary Christian tradition:
I heard a priest once say the fires of hell and the pain of purgatory weren't literal fire, but the burning pain of regret around unhealed or unresolved harmful actions.