Since our goal and the purpose of life is happiness, what is happiness? Sometimes physical suffering can even bring a deeper sense of satisfaction like with an athlete after a gruelling workout. So “happiness” means mainly a sense of deep satisfaction. The object of life or our goal, then, is satisfaction.
Happiness, sadness, or suffering—for these, there are two levels: a sensorial level and a mental level. The sensorial level is common with tiny mammals, even insects—a fly. In a cold climate, when the sun comes out, a fly shows a happy aspect: it flies around nicely. In a cold room, it slows down: it shows a sign of sadness. But, if there is a sophisticated brain, then there is even a stronger sense of sensorial pleasure. In addition, though, our sophisticated brain is the largest in size and, therefore, we also have intelligence.
Consider the case of humans who feel no physical threats. They have a happy, comfortable life, good friends, salary, and name. But, even then, we notice that some millionaires, for example—they feel that they are an important part of society, but often these people as persons are very unhappy persons. On a few occasions I have met very rich, influential people who showed a very troubled sense that, deep inside, they had a feeling of loneliness, stress and worry. So, on the mental level, they have suffering.