In my previous two columns, I discussed the importance of having a sense of meaning in one's life.
I said that without a deeply felt sense of purpose, even the most comfortable lives can feel sad and empty; and that with such a sense of purpose, even the most outwardly wretched lives can feel worthwhile.
According to the Austrian psychiatrist and Holocaust survivor, Viktor Frankl, there are three sources of personal meaning: Work, love and courage.
When Frankl was a prisoner in the Nazi concentration camps of World War II and was tempted to give in to despair, two things gave him the will to struggle on.
One was the thought that, one day, he would help others by speaking and writing about the psychological lessons he had learnt in the camps.
He believed that he had an important work to do - a work that nobody else could do, a work that would be of great benefit to others.
This belief gave him a reason to carry on and to try to survive.
The same holds true for us all.
When we are focused on a goal - something that truly motivates us and requires us to use our talents and skills to the full - we feel that life is worth living.
In Man's Search For Meaning, Frankl wrote: "What man actually needs is not a tensionless state, but rather the striving and struggling for a worthwhile goal, a freely chosen task."
The specific goal hardly matters. It varies from person to person.
The important thing is the deeply felt desire to achieve it.
For example, last year, I spent three months walking the length of Britain. Those were three of the happiest months of my life.
Not because the task itself had any profound significance.
But because, each day, I was able to enjoy the feeling that I was making progress towards a challenging and freely chosen goal.
According to Frankl, "the second way of finding a meaning in life is by experiencing something - such as goodness, truth and beauty - by experiencing nature and culture, or, last but not least, by experiencing another human being in his very uniqueness - by loving him".
People have the capacity to love all kinds of things. Some of us have a deep love of nature.
Others feel the same way about music, mathematics, literature, art, history or sport.
When we are absorbed in something that we love - just as when we are focused on an important goal - we are fully engaged in life. We feel, at least for the moment, that life is worthwhile.
This is especially true when the object of our love is another person.
The second thing that gave Frankl the will to survive the concentration camps was the thought of being reunited with his wife after the war.
In his darkest hours, he would cling to her image.
He would recall her kind words, encouraging look and loving smile.
In doing so, he said, he came to appreciate, for the first time, the age-old truth that love is the highest goal to which a human being can aspire.
Love, more than anything else, brings a sense of meaning to our lives.
The third source of personal meaning, according to Frankl, is courage.
As a concentration-camp survivor, Frankl knew better than most that people are sometimes trapped in situations in which they cannot realise their values through creative work; in which they cannot find fulfilment through experiencing beauty, art or nature; and in which they cannot share love with those who are most dear to them.
They are placed in situations in which there is little they can do but to endure the suffering.
Even at such times, Frankl said, people can bring a sense of meaning to their lives by meeting their fate in a brave, dignified and unselfish manner.
In Man's Search For Meaning, he recalls those prisoners who would walk through the huts, comforting others and even giving away their last piece of bread.
He wrote: "They may have been few in number, but they offer sufficient proof that everything can be taken from a man but one thing: The last of the human freedoms - to choose one's attitude in any given set of circumstances, to choose one's own way."
As someone who sometimes suffers from a sense that life lacks meaning, I find those words inspirational.
They remind me that even at times when life does not feel meaningful, it is still possible - through work, love and courage - to live a meaningful life.
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