When I hear about the word cheerfulness... all I have to do is just think about the difference between people living in the rural parts of the country, compared to people living in the city. Which of the two are more cheerful and peaceful? I would say that most of the time, it is the people living in the rural parts that are more cheerful.
Why? because of simplicity. Through simplicity, we can experience our mind in it's raw state, unaffected by many of samsaric's distractions... and along with the Dharma, we begin to trust our mind and discover the inherent goodness in it.. thus leading us to be more cheerful. Cheerfulness is the natural state of mind, that is why with meditation, when the mind is relaxed and have space... we will find ourselves to be in a state of genuine cheerfulness.
Being in the samsaric world, where we are often forced to put on a cheerful expression, we do this because society tells us to put on this expression so we force it, and hope that nobody (including ourselves) will realize the that we are actually not happy. Then through this, we will crave more... we will be more attached. Why? because the happiness is not genuine and deep down we know it is not genuine so we tend to try very hard to keep it because we're afraid losing it will make us unhappy.
Then there is another type where people prevent themselves to feel cheerful. Some people feel if the abstain for feeling cheerful, we will prevent ourselves from the pain when the cheerfulness come to an end, thus we end up becoming defensive, feeling that we're protecting ourselves.
Under these conditions, we will find that the lack of genuine cheerfulness results in a claustaphobia mind and a closed heart which causes the ups and downs of our mood. Why? Because somehow we had an impression that life should be perfect, and so far we're not experiencing that perfectness... so we end up contorting reality into our fantasy happiness... which leads us to more unhappiness.
Life will always rise it's painful, ugly head... That's why we must take into account and accept the harshness of life. We must counter these painful moments with cheerfulness, not by ignorance but through wisdom. After all, contemplating on the truth of pain and suffering does not make one have depression. Instead, it helps us appreciate what we have.
Just remember a saying that goes "the joy of a King is no greater then the joy of a beggar". It is not about what we own, but cheerfulness comes from what we enjoy... therefore it cannot be bought or sold, and the only thing that can bring about genuine cheerfulness is through being free from fixation and attachments.