Ever since I fell victim to depression in 2008, happiness is a subject I’ve been much preoccupied with.

Why do people who outwardly have similar lives to me feel content and at peace, while I wake up every morning hating my existence? I used to think.

Part of the reason was because I was suffering from an illness that needed treatment. But I knew that another reason was because I, to put it simply, didn’t know how to be happy. For whatever reason, I didn’t know how to act, think or make decisions in a way that would lead me to enjoy my life.

7 hacks for a healthier week

So I dedicated myself to the study of happiness. I talked to doctors, therapists, my parents and my friends; I read self-help and personal development books; I analysed the behaviour of athletes, artists and entrepreneurs who lived successful, fulfilling lives; and I travelled to five different continents to talk to people from all walks of life to find out what makes them happy.

Need a smile? These quotes will do the trick.

Over time, I learned a lot, and combined with getting the treatment I needed, I managed to recover from depression, and these days, I’m blessed to be able to say that I live a very happy and healthy life.

In light of what I’ve learned over the years, I’ve put together a list of 15 things I believe that people who are happy do differently from people who aren’t.

The good news is that these qualities don’t need to come naturally. I can tell you first hand that they are skills that can be learned.

1. Happy people are aware of their core values and build their lives around them.

Happy people know exactly what makes them happy and exactly what doesn’t make them happy – and they structure their lives in such a way so that they maximize the time they spend doing things that make them happy and minimise the time they spend on doing things that don’t make them happy.

2. Happy people learn from their mistakes and from difficult times.

Everybody will make mistakes – in their career, in their relationships, with their finances, and in every other facet of their life. But happy people make sure they learn from their mistakes and from difficult times so they don’t continue to repeat themselves over and over and over again.

11 things Jesinta Campell does to feel happy, every day

3. Happy people don’t care about what other people think of them.

No matter what you do, there’ll always be people who don’t like you, who will judge you, or who will criticise you. Happy people understand this, and what’s more, they understand that worrying about what other people think of them is wasted energy that could be better spent elsewhere.

4. Happy people are grateful for what they have.

This really hit me when I did volunteer work at an underprivileged school in Peru, at an orphanage in Cambodia, and in a slum in India. The majority of people I met were happy, friendly people – because they focused on and were grateful for what they had, instead of wasting their energy dwelling on and pining for what they didn’t have.

5. Happy people don’t try to please everyone.

This is an impossible goal, so happy people don’t stress about trying to achieve it.

6. Happy people don’t worry about things that are beyond their control.

Few things come more naturally to us than worrying, but once we learn not to stress about things that are out of our hands, it frees up a lot of energy that can be better spent on something more positive.

7. Happy people know how to let go of anger.

As the saying goes, holding onto anger is like drinking poison and expecting someone else to die. The only person it hurts is us.

The 15 most passive-aggressive inspirational quotes we’ve ever seen

8. Happy people understand they are not the centre of the universe.

As a result, they understand that the way someone else reacts to them may well have nothing to do with them – so they don’t sweat it too much.

9. Happy people don’t victimise themselves.

Bad things happen to everyone, but happy people understand that feeling sorry for themselves won’t get them anywhere. So when something bad happens, they confront it, resolve it and then move on from it – instead of doing nothing and forever feeling like a victim.

10. Happy people surround themselves with positive people

To varying extents, we're all influenced by the people around us. If we surround ourselves with positive, inspiring people, then we tend to feel positive and inspired. On the other hand, if we surround ourselves with negative, downbeat people, then we tend to feel just that.

11. Happy people live a healthy lifestyle.    

You'll meet few happy people who don't make a point of eating well, sleeping well and exercising frequently. It's almost a law of nature.

12. Happy people aren’t so obsessed with trying to make a living that they forget to make a life.

Making money's important, sure - but we shouldn't work so hard at filling our bank accounts that we forget to enjoy ourselves.

The 7 ridiculous questions that will lead you to your life’s purpose 

13. Happy people don’t dwell on the past.

Bad things happen – it's just the way life is – and the more we ruminate on the past, the more we allow it to destroy our future. It's better to accept it, learn from it and then move on from it.

14. Happy people don’t waste time comparing themselves to other people.

Life is not a race. There's no need to worry about what everyone else is doing, because it isn't relevant to us.

15. Happy people are pro-active.

Happy people don't believe that the world owes them anything. As a result, they are proactive, and believe that everything they want in life, they have to work for. Including happiness.

How do you keep happy?