Why is desire the root of suffering? I fail to understand how this teaching would ever help man become productive. Please help me understand this.

Not everyone seeks nirvana and some people want to better the world, not only for themselves but for their family and countrymen. They do so either out of desire to reduce others' suffering or by seeking alleviation for their own sufferings. I've read a lot of self help books which emphasize the need for desire as such, and faith in oneself to achieve that desire. Is that not how every living being functions - driven by desire?

Every business that is built is motivated by a desire. Every material possession is obtained through desire. We can extrapolate that to the spiritual realm by saying that man travels, meditates and watches his thoughts driven by a desire to attain spiritual peace and fullfilment.

Thus I ask, how can desire be the enemy? Shouldn't it be greed instead?
Working on your hobbies, advancing your career, growing a business, developing a family, nurturing a child, improving your health through good diet and exercise, going on vacations, increasing your wealth, using your money for the enjoyment or development of yourself and others, raising your status in the world, attaining fame in society etc. could all make you happy.

It would not just make you happy, but also your family and people around you. If you start a business, you might create jobs for others. If you buy goods and services, you sustain others' income.

All these types of worldly happiness definitely need sensual cravings (kama tanha) and cravings of becoming something (bhava tanha).

Buddhism teaches the pursuit of happiness and the elimination of suffering (dukkha). The short term happiness goal in Buddhism is worldly happiness, when it is achieved through virtue, merit, charity and harmony. Also see this answer to the excellent question "Can a Buddhist own and run a billion dollar business?".

Here's another example of a sutta where worldly happiness is preached in Buddhism. From AN 5.58:


  He always does his duty toward his parents;
  he promotes the welfare of his wife and children.
  He takes care of the people in his home
  and those who live in dependence on him.
  
  The wise person, charitable and virtuous,
  acts for the good of both kinds of relatives,
  those who have passed away
  and those still living in this world.
  
  He benefits ascetics and brahmins,
  and also the deities;
  he is one who gives rise to joy
  while living a righteous life at home.
  
  Having done what is good,
  he is worthy of veneration and praise.
  They praise him here in this world
  and after death he rejoices in heaven.


However, worldly happiness is a short term type of happiness. Nothing ever lasts.

Your health and youth would not last forever. Your loved ones or friends may forsake you. Your career or businesses may dwindle. Your money and possessions may get stolen. Your peaceful life in your country may be replaced by civil unrest.

No one knows this better than the Buddha, who was a prince who had everything. Realizing that worldly happiness would not last forever, he set out to find permanent happiness and eventually found it. To achieve permanent happiness, you must uproot craving.

There are three types of craving (tanha): craving for sensual pleasures, craving to become something (that makes someone have ambition) and the craving to not become something (that makes one suicidal or withdrawn).

If you crave for food, and eat some tasty food, you may cling to it or become attached to it. You think and fantasize about it even when it's not there. That's clinging or attachment. Craving gives rise to clinging and clinging gives rise to greed or lust to acquire it.

If someone prevents you from getting the tasty food that you cling to, then you feel angry. That hatred or aversion arises because you were denied what you cling to.

If this anger makes you enraged that you go and harm this person who prevents you from getting what you want, this is delusion. Delusion clouds your better judgment.

The craving to become something is similar. Examples are like wanting to get a gold medal or to get a promotion or to become doctor or professor or get recognition etc.

If you crave to get recognition and get it once, you may cling to it and want it even when it's not present. This leads you to do things to get recognition as you have greed (or lust) for it.

If you don't get recognition, but someone else does, you become envious. That's aversion.

If continuously not getting recognition leads you to become depressed, which clouds your normal healthy state of mind, then that's delusion.

That is how craving is the root of all suffering. When you uproot craving, you will uproot suffering.

Of course, it is not a MUST that you seek the permanent happiness of Nibbana. If you are only seeking the short term type of happiness, that is worldly happiness, make sure you include virtue, merit, charity and harmony. At the very minimum, the practice of the five precepts is needed.