Clinging, or attachment, is what keeps us suffering. As soon as we truly accept that all things are impermanent, our suffering will end. The 4 Noble Truths are as follows:
1. Life is suffering
2. The origination of suffering is attachment
3. The end of suffering is attainable
4. The path to the end of suffering is the realization that all things are impermanent
I para-phrased #4 because if refers to the Eight-fold Path and I don't want to bore you with details.