The American author Mark Twain once wrote: "The two most important days in your life are the day you are born and the day you find out why."

This raises several important questions: what do you love doing? What is your real purpose? Why are you here, doing what you're doing, right now?

A little while ago I was in Antigua, Guatemala, one of my favorite places on the planet. I fell in love with the watercolors of a street artist called Gerardo, who was working around the clock to produce wonderful landscapes. I wanted to buy one of his works of art but he had none left, except the one he was working on, which was unfinished. As I was leaving the country, I could not wait, so I insisted on buying the watercolor and asked him for a discount, since it was not finished yet.

Labour of love: Gerardo's painting

Gerardo asked me for twice the price he normally charged. I was surprised and somewhat upset; and asked him why he was charging me double for something incomplete. Gerardo replied: “Because you're taking away from me the joy of doing something I really love.” I paid him what he asked for, knowing that I got a priceless lesson in life. If someone has to pay you to stop doing something, you really love what you are doing.

Do you love what you do?

Being able to keep hold of your passion and hone your talent remains a cornerstone for a career of significance. If you love what you do, the effort you put into it will become a pleasure.

Steve Jobs, the founder of Apple, said in his commencement speech at Stanford University in 2005 that we should look in the mirror each morning wondering: "If today were the last day of my life, would I want to do what I’m about to do today?" He added that, if the answer was negative for too many days in a row, it would be time for a change.

From Steve Jobs to Snoopy

Finding a passion and sustaining it over the whole course of your career isn’t easy - but nor is it impossible. Charles M. Schultz, the legendary creator of Charlie Brown and Snoopy in the comic strip Peanuts, poured passion, love and creativity into the same job for 50 years.

He began publishing his cartoons in 1950 and in 3 January 2000, after half a century of extraordinary success, he decided to retire and end the comic strip, because “my family does not wish Peanuts to be continued by anyone else”. In his last cartoon, Schultz wrote that drawing Peanuts had been the dream of his life. He died at the age of 77, the day before the publication of his last strip on February 12, 2000. The final strip is a tender and moving vignette, and a clear declaration of love for what he had done 17,897 times in 50 years.

Finding what we love and making it our life’s work helps us to excel, to stay happy and to remain young in our minds. Picasso created hundreds of artworks as an octogenarian. Bruce Springsteen is still arguably the best rock artist on earth after 40 years. If you see him playing, you will understand that he loves what he does. At the age of 86, Gualtiero Marchesi is an artist as well as a chef, integrating beauty with the most refined taste. Passion is not confined to the young; it keeps us young. Think of the entrepreneurs, artists and writers at the height of their powers of expression, even at a very advanced age. Instead of wearing them out, work sustains them. As Confucius put it:

“Choose a job you love, and you will never have to work a day.”

How can you tell if you love what you’re doing? Back in 1961, the Hungarian psychologist Mihaly Csikszentmihalyi described the state of being happy: he called it “flow”, referring to the sense of focus that comes when you are immersed in activities like art, play and work.

Look at children when they play: they are so intensively focused on that one activity, they forgot the world around them. They are in a state of flow; or “in the zone”. We might not - one hopes - be building tree forts or playing hopskotch in the office, but that joyful absorption in what we’re doing still holds lessons.

Let’s pause for a moment and think of what we were doing when we were last in the zone. Which activities were we performing? If, for example, we return from the office feeling exhausted but, as if by magic, we find a renewed sense of enthusiasm when we start a new activity, whether it’s learning a language or volunteering for a cause that’s important to us, it might help us point our careers in a new direction.

Whether you call it flow or being in the zone, the ability to absorb ourselves completely in the here and now is the meaning of happiness, and it we’re lucky, it can underpin a lifelong love of what we do.