The Power of the Mind - By His Holiness the Dalai

The source and cause of peace and happiness is the mind.Both positive and negative experiences arise from the mind, depending on whether your mind is transformed or not. Therefore, it is most important to control and discipline the mind. All the fears and the immeasurable suffering that we encounter arise from the mind. The Buddha taught that there is no enemy more powerful than the mind. In all the realms of existence, there is nothing more frightful—nothing more to be feared than the mind. Likewise, he said that the disciplined mind gives rise to all excellent qualities. The source and cause of peace and happiness is the mind. Happiness arises from virtuous practice; sufferings arise from negative practice.

So happiness and suffering depend upon whether your mind is transformed or not. Even in the short term, the more you control and discipline your mind, the happier and more relaxed you will be. Once the mind within is controlled and relaxed, even if the whole universe appears to turn on you like an enemy, you will not feel threatened or unhappy. On the other hand, if you are internally disturbed and agitated, even if the most delicious food is laid out on the table in front of you, you will not enjoy it. You may hear pleasant things, but they will bring you no joy. So, depending on whether your mind is disciplined or not, you will experience happiness or suffering.
Once you transform your mind so that you have no possessiveness and no craving, you will achieve the perfection of giving. The perfection of giving means that you offer everything that you have, as well as the positive results of the offering, to all sentient beings. The practice is entirely dependent on the mind. The perfection of ethics is similar. Achieving the perfection of ethics means that you attain a state of mind that refrains from harming sentient beings in any way at all. It is a state completely free from self-centeredness. The practice of patience is the same. Unruly sentient beings are as infinite as the extent of space. However, once you control your own mind, it is as if you have destroyed all external enemies. If your mind is calm, even though the whole environment is hostile, you will not be disturbed. To protect your feet from thorns, you cannot cover the entire surface of the earth with leather.