The more grounded we are and willing to face those "inconvenient truths", the closer we come to truth and happiness, suggests Eric Harrison.

We think of wise people as being grounded, down-to-earth, in touch with reality, and willing to call a spade a spade. They disdain hype and spin, and unerringly hone in on the hard facts of any matter. They can't help but see things "as they really are".

This doesn't make them popular or admired, however. The truth is often inconvenient, as Al Gore says, and about as welcome as a brick wall. The Book of Tao says a wise man is unsophisticated and close to nature, like an uncarved block of wood. Wisdom often has a childlike, gauche quality that can be offensive to our fondest hopes and illusions.

The Book of Tao also says that if stupid and powerful people did not ridicule the truth, it would not be the truth. I personally have arguments with the wise part of me all the time: 'Of course I know that, but . . .' Although the facts may be perfectly obvious, I prefer to hope and dream. Unfortunately, the hard facts usually win out in the end.

For example, we are made of earth and will return to earth. "Ashes to ashes, dust to dust," says the Bible. Our bodies and brains and even our thoughts are all constructed from the same elements that we find in a handful of dirt. Of course, the miracle is in the way they are combined. Although every living thing is infinitely more than the sum of its parts, we still can't do without the raw ingredients.

Some combinations of elements make giraffes and mosquitoes. Others make symphonies and cruise missiles. Some construct God and economic theories. All of these are utterly reliant on atoms of hydrogen, oxygen, carbon, nitrogen and a few trace elements. All will dissolve when the atoms that form them go their separate ways, as they inevitably do in time. As the Buddha said, "Everything that has form is bound to decay".

It is both self evident and profoundly shocking that nothing lasts for long, with the exception of the atoms themselves. Even the most perfect idea or spiritual concept has a limited life span. Mythology is littered with the corpses of "immortal" gods.

This quandary is at the heart of philosophy and religion. Heraclitus said, "You never step into the same river twice". He said that the nature of life is to perpetually consume itself, the way that fire does. The Buddha said that a deep understanding of transience is the wisdom that prompts you to forever reject the world.

Parmenides, on the other hand, said that death is an illusion. He said that it is impossible to imagine not being here. In whatever way we try to imagine being dead, we have to be alive to do so. 'Death' is therefore a logical impossibility. In fact, said Parmenides, we live forever and nothing ever changes.

We can all sympathise a little with this absurd idea. We instinctively feel that something must be eternal, be it God or the soul or the cosmos or the law of physics. There must surely be something solid and enduring under our feet. Unfortunately, not even our profoundest convictions are necessarily true. Even though our imagination can effortlessly fly in the realm of the eternal, the Earth literally drags us down. Our bodies are heavy. It takes vast amounts of energy, 2000-3000 calories at least, to hoist our 60 or 100 kg out of bed in the morning, and cart it around all day long. No matter how much food and coffee we consume, we have to periodically submit to gravity, and let the Earth and the night claim us. One day, they will claim us forever.

Although our spirits fly, we are hostages to the Earth. We all need a place to stand, to lie down on at night and a place to work. Yet, how secure do you feel on the ground you now occupy? For most of human history, that right to be here was self evident. If you were born in a village you were automatically a part-owner of the common land, and of the pastures and forests around you. No one could tell you to move on. That was your place.

We tend to take this right for granted, but for some half a billion people throughout the world, it is not that easy. Immigrants, refugees, the people on temporary visas, the newly arrived slum dwellers, all strive to occupy and feel safe on their own little patch of earth. It can be a desperate struggle to pay for the twelfth part of a room, or even a body's length of filthy pavement at night. Nothing is free for those who have no legal rights.

As an immigrant myself, I was delighted when I could purchase my flat in Subiaco, in Perth's western suburbs. The day after I moved in, I realised I saw the suburb differently. As a ratepayer, I now partly owned the streets, the lampposts and the parks. I had purchased my right to be here. But I also know that as a citizen of the First World, I am depriving others of that right. The more land I take, the less is available for others, and I'm not just talking about my flat.

Each day, I consume about a hundred times more of the world's resources than the average Nigerian. My lifestyle has a large footprint. It requires factories and farms and oil wells in foreign lands. I demand climate warming carbon emissions every time I send an email or buy a tomato or make a phone call. Altogether, my lifestyle requires the produce of a hundred times more land than the Nigerian is obliged to scrape by on.

I live a modest life by First World standards, yet this level of per capita consumption already exceeds the carrying capacity of the Earth. If everyone on the planet lived like me, we would need the produce of three or four Earths to support us all. And there would be no room for wild animals.

Although economies boom on credit, and my shares irrationally increase in value, the world resources are always finite and shrinking. As those resources decline through overuse and plunder, this means that the rich (that is, you and me) require an ever-increasing percentage of the world's productive land to support us. We do this at the expense of the poor, who literally lose the ground under their feet. In practice, they flee or are driven from the dying countryside, and have no option but to battle for a toehold in the world burgeoning megaslums.

Fortunately, this doesn't mean that the poor have to be miserable. One simple requirement for happiness is to live in and for the present, whether we live in a slum or a palace. We can't postpone happiness till retirement or even until the weekend. We find it in this cup of tea, or this can of beer, or not at all. Yet this truth has a very dark side to it. For the sake of happiness, we ignore the long-term consequences of our actions, as we have always done. Ever since our first ancestors emigrated from Africa, we have exterminated the big animals, killed the last fish, cut down the last tree and stripped the soil from wherever we were, for immediate advantage. After all, if we didn't, someone else would.

Since the birth of agriculture only 7000 years ago, we have destroyed more arable land than we currently have available to us. It is quite possible that there is no such thing as sustainable agriculture, except in theory, if we calculate all the costs. Even the most benign forms of farming seem to eventually degrade the earth and damage the environment they rely on.

Although our human cleverness is also a curse, we no longer have any excuse. Even the most short-sighted politicians now know that we have to listen to what the planet is telling us, or face the consequences.

Similarly, we each have to listen to that small part of planet Earth that always belongs to us, namely our own bodies. Our brains are enormously clever and can process vast amounts of data, but only our bodies can make sense of it all. We can't reason our way to wisdom. The issues are too complicated.

Our thoughts are noisy and cocksure but, far below the surface, our bodies are always telling what is good or bad, true or false, valuable or useless. These messages are faint and subtle, but invariably accurate. The body doesn't lie, although we can easily ignore or misinterpret what it tells us.

Whether we are rich or poor, the essence of good judgement is to be grounded in our bodies, in touch with reality, and to be willing to face the inconvenient truths. It pays to be down-to-earth and to call a spade a spade. Hoping for the best, like living on credit, is much more attractive, but the hard facts can't be avoided forever.