What we are contributes more to our happiness than what we have or how we are regarded by others.

So claimed German philosopher Arthur Schopenhauer (1788-1860).

In other words, our happiness depends, to some extent, upon what we earn and what we own.

It also depends, to some extent, upon our status and reputation.

But it depends, most of all, upon our personal qualities, such as health, strength, temperament and such like.

There is a lot of truth in that.

Two people can lead quite similar lives, as far as circumstances go. Yet, to one, life is full of interest and meaning while, to the other, it seems dull and barren.

The difference lies not in what the world brings to them, but in what they bring to the world.

The upshot of this, says Schopenhauer, is that we should make it a priority to develop our inner selves.

He writes that subjective blessings - a noble nature, a capable head, a joyful temperament, bright spirits and a well-constituted physique - are the first and most important elements in happiness.

We should be more intent on promoting and preserving such qualities than on the possession of external wealth and external honour.

Schopenhauer adds that of all the inner qualities, the one that is most conducive to happiness is a cheerful attitude.

If we are blessed with a joyful temperament and bright spirits we will meet the circumstances of life - both the good and the not-so-good - in a robust and positive manner.

We will have every chance of happiness.

Our chief aim then should be to secure and promote a cheerful attitude.

But how is this possible?

If we are not naturally blessed with bright spirits, what can we do to develop them?

In an essay titled On the Wisdom Of Life, Schopenhauer offers a number of strategies for developing cheerfulness.

By far the most important one is to maintain good health.

He writes that it is certain that nothing contributes so little to cheerfulness as riches, or so much, as health.

Consequently, we should try as much as possible to maintain a high degree of health; for cheerfulness is the very flower of it.

In practical terms, this means avoiding "every kind of excess", all "violent and unpleasant emotion" and "mental overstrain".

It also means taking "daily exercise in the open air".

In doing so, we give ourselves the best possible chance of maintaining good health, and increase our chances of happiness.

When we are strong and healthy, we find it easy to enjoy life's pleasures.

But when we are weak and sickly, we find it difficult to enjoy anything.

MAKING HEALTH A PRIORITY

At this point, some readers might complain that both Schopenhauer and myself are guilty of stating the obvious.

After all, everyone knows, already, that good health and happiness are interlinked.

But, of course, it is not enough to simply know it.

We all know the importance of moderate exercise, fresh air, sleep, rest and relaxation.

But do we make those things a priority?

It is all too easy, in the hurly-burly of life, to let those things slide.

I recently read the autobiography of the English businessman and producer for radio and television, Chris Evans.

In it, he remarks that when life gets difficult, there are three things that you will not want to do, but that you must do: Make sure you get enough sleep, eat well and exercise.

Great advice, I think.

• Gary Hayden is a philosophy and science writer.