Why men are grouchy but not children?

You must have observed new born babies smile frequently without any apparent reason. They smile any number of times a day and even during their sleep. When it sees a simple toy, its mom’s face or for that matter any known face, it breaks into a smile. When it hears a rattler or sees a bird or any colourful thing its face beams. Smile for it is a state of happiness and contentment. It derives happiness at simple things. It has no expectations and is contented.This frequent smile fades slowly as it grows older. Look at the grown up men. They rarely smile as they are always in a state of unhappiness. They crave for more money, more comforts, and more wealth and in some cases for more women. They are not satisfied with what they possess and are driven by greed and passion. When they fail to realise what they wish for, they become worried, tense and grouchy driving away happiness and contentment.
Happiness comes about if we are thankful to the God for our blessings instead of bemoaning at our wants. We can compare ourselves with the less fortunate and be grateful for the gift of good health, keen mental and physical faculties and for the good family and friends. But we rarely do this crying over what we have not been blessed with. We always forget that happiness doesn't come as a result of getting something we don't have, but only by recognizing and appreciating what we have. We must realise that there is no end to craving and desire and that happiness can be acquired only by contentment. This does not mean that you should lead a life of sanyasin.You can have normal ambitions in life and legitimate desires .You can acquire wealth to live in comfort and help the needy but not be greedy, you can marry to lead a happy married life but not be driven by lust and you can exercise power to do good to others but not to harass.
“Contentment is natural wealth, luxury is artificial poverty.”