One of my all-time favourite thinkers is Greek philosopher Heraclitus (535-475 BC).
By Gary Hayden
Not so much because of his ideas - though he had some very profound ones - but rather because he was so deliciously eccentric.
He was the archetypal grumpy old man.
He lived in a state of permanent irritation at the stupidity and corruptness of his fellow citizens.
So much so that eventually, he went into the mountains to lead a solitary life surviving on a diet of grass and plants.
Unfortunately, this back-to-nature lifestyle did not agree with him.
He ended up suffering from dropsy, an abnormal accumulation of fluid beneath the skin.
He returned to the city and consulted some doctors, but they were unable to help him.
This was hardly surprising as he explained his symptoms to them in the form of a riddle.
The upshot was that he tried to treat himself by lying in a stable and covering himself with cow dung.
Whereupon, he died.
It was a sad and ironic end for a man whose philosophical theories stressed the need for people to live together in social harmony.
Heraclitus is a textbook example of a misanthrope, a person who dislikes or distrusts other people or mankind in general.
He is, of course, an extreme example.
There are few people in the everyday world whose dislike of others leads them to shun society, live off grass and cover themselves with manure.
But nonetheless, there is no shortage of misanthropes, of a milder variety, out there.
Some time ago, I met a woman in a cafe who used to be in the same class as I was at school.
I began to reminisce about some of our old schoolmates and said how lovely it would be to see them again.
'I wouldn't want to see any of them,' she replied. 'I hated everyone at school.'
Here is another example.
I spoke to a man in England recently who told me that he was suffering from high blood pressure and that the doctors could not identify the cause.
'I know what it is, though,' he said. 'I sit at home and I get to thinking about the state of the world. It makes me angry and I brood and brood. That's what's causing it all.'
Of course, it is not the world itself that he is angry with.
It is the people who live in it.
He has become disillusioned and disappointed with mankind in general.
What makes people misanthropic?
People are complex creatures. So doubtless there are many and varied reasons why people grow to dislike and distrust others.
But one interesting and plausible explanation of the misanthropic temperament comes from the Greek philosopher Plato, who came a hundred years or so after Heraclitus.
He said: 'Misanthropy develops when without art (that is, naively) one puts complete trust in somebody thinking the man absolutely true and sound and reliable, and then a little later discovers him to be bad and unreliable... and when it happens to someone often... he ends up... hating everyone.'
In other words, the misanthrope falls victim to his own unrealistic expectations about how other people can be expected to behave.
Most of us realise that other people are sometimes selfish, lazy, unkind, shallow, stupid and ungrateful.
Even the best of them are sure to disappoint us from time to time.
Just as we disappoint them from time to time.
Being realists, we accept this and try not to get too worked up about it.
Not so, the misanthrope.
His naivety, or misplaced optimism, or whatever it is, sets him up for disappointment after disappointment and leads eventually to bitterness and disillusionment.
The misanthrope would be wiser to expect a little less from others.
Sure, people do not always behave as they ought to.
And some people behave very badly indeed.
But we ought to have some respect for human frailty and remember that most men and women are neither terribly good nor terribly bad.
The Dutch philosopher, Baruch Spinoza (1632-1677), showed marvellous good sense when he urged: 'Do not weep; do not wax indignant. Understand.'
Gary Hayden is a philosophy and science writer.