Laughter Yoga is a body-mind approach to health and wellness that helps people redefine happiness as a choice and not a consequence. Inherently it means nothing and therefore there is nothing to explain. Therein lies its very strength.
Never mind how hard it has been for you to do so. Smile now! If you will remember all the time to smile now, you will smile always. However, a mechanical smile will not do. Your smile should be a reflection of your inner soul state of ever new joy.
We are what we think we are. The habitual inclination of our thoughts determines our talents and abilities, and our personality.