"I want to be happy” is a universal goal in our lives—as a baby or as an elderly person. For one person, happiness lies in accumulating many possessions; for another, happiness lies in leading a simple life and serving others.
The Yogasutra says that the purpose of yoga is to remove duhkha or suffering. Removing unhappiness is no doubt attractive. Yet, all of us would like something more. All of us would like to be happy.
Happiness and unhappiness are both just experiences in our mind—like all experiences, they are transient. Happy moments pass, leaving behind pleasant memories. On the other hand, unhappy moments usually pass too, leaving behind unpleasant memories.
When we are happy, our mind is excited and active. The mind cannot continue to remain like that all the time. We would find it tiring after a while. Eventually, the excitement of happiness or pleasure gives way to a feeling of satisfaction or contentment. Then our mind gradually becomes restful, relaxed.
“Being happy” is temporary. “Being fulfilled or content” is potentially long-lasting.
The Yogasutra does not say “I will show you how to be happy,” because that is a transient goal. Instead, it says, “I will show you how not to be unhappy.”
To be free of unhappiness does not mean that we are never happy. It means that we are peaceful within; that we have restful contentment instead of the mental urge to chase happiness without pause. That is a lasting goal.