Each and every phenomenon has its own causes and conditions. All the pleasures and happiness arise from virtuous deeds, and conversely, all the pain and suffering from non-virtuous deeds, including rebirth in the lower realms. To be free from suffering, you must abstain from the causes which are the non-virtuous deeds. Even a small negative deed should not be ignored because it will accumulate and later cause much harm, like a small spark of fire having the capacity to burn down the whole forest. Just as an accumulation of drops of water can become an ocean, similarly, seemingly insignificant virtuous deeds can accumulate to form a significant virtuous deed.

-- His Holiness Sakya Trizin