It is difficult to define happiness, for it cannot be measured. Happiness is a state of mind just like health is a state the body.
Health has been defined as a healthy state of well-being, free from disease or abnormality.
Let us define happiness as the state of contentment when a person is free from all unhappy emotions like pain, misery, frustration, boredom, hatred or depression. This definition resembles the definition of health. Just like a healthy person is one who is free from any ailment, a happy person is one who is free from any suffering.
In short, we are happy if we are not suffering from unhappiness. This state of happiness is achievable like it is possible to avoid sickness or ill health by following the right lifestyle.
When we are trying to achieve something in life, we may find ourselves in a state that gives our mind tension or anxiety, but we should not confuse this state of unhappiness because we are actually in the process of attaining happiness. When we work out in the gym, we find that we sweat, our blood pressure and heartbeat increase and our body may ache. But this is not a sigh of poor health because you yourself have let it happen in your pursuit of good health. In the same way, when we ae doing something for the happiness of the body, mind or soul voluntarily, it may give us temporary suffering, which is not unhappiness, but an investment likely to bring us more happiness in future.
Hence, when you strive for something that gives happiness to your mind, intellect and soul, you are ready to undergo suffering, and it shall not cause you any unhappiness. For example, when you work hard in order to secure the top rank in an examination, the hard work does not annoy you for you are aiming at a greater state of happiness.
Mahatma Gandhi was not unhappy that the struggle to make India independent failed initially and he had to spend many years in prison for he knew that he was moving on the right path and would meet his goal one day
The true test of happiness is that you should anticipate and accept your pain and suffering rather than have it forced upon you against your will. It is only when you have a clear conscience and deep faith in God that you attain a deep understanding of yourself and of the world, and a sound knowledge of the laws of the world.