Complete happiness is impossible to achieve as long as you are living in a society. Because our mind never gets satisfied with what we have achieved in life. It will always keep craving for what we don’t have. For some it could be money, or health, or time to spend with family, or a better spouse, or obedient children or more & more money.
No body gets everything in life and therefore its useless to aim to satisfy mind and achieve complete happiness.
The best you can achieve is when you stop craving for material things and learn to live alone. Mostly cut off from the society. Don’t expect anything from your spouse, children, or even god. Because if you are not expecting something from your family, or boss, or community, then you can not fail and you can not get disappointed with anyone.
Simply witness the short events of happiness and sorrow while not getting too much excited or depressed about these life events. They are but two sides of the same coin. And nothing is permanent. They keep coming and going.