Happy people vs unhappy people

Have you ever wondered why some people are constantly happy while others are constantly unhappy. Why some people look forward to each day with renewed zest and passion while some live in angst and fear?
I had a rather interesting conversation today with someone. And this topic came up. So before i go on to tell you what the gist of the conversation was, let me pose you this question. If today, you were an athlete, or in school, or at work for that matter. And you were lets say taking half hour to run your 2.4km, or getting 40 marks in school, or earning $20,000. Would you be happy? This is considering your peers were taking 10 mins to run their 2.4km, getting 90 marks and earning $70,000. And should you have an improvement, lets say you were getting better, 20 minutes for ur 2.4km, getting 70 marks, and earning $40,000. Would you be happier along the way, or sad that you are still not catching up with your peers?
I suppose everyone has a different sort of thinking and everyone will have their own forms of justification as to why they think in certain manner. Here's the thing, the people who are happier are usually the people who give themselves a pat on the back every time they improve and keep working towards greater improvement every day. They are the ones who wake up with renewed zest and passion and strive for greatness. While the second group of people, live in angst and fear. Fearful that they might never match up, fearful that they would not progress. And for some, fearful that should they put in their best, they would still not match up and be totally disheartened by it.
Let's say both groups of people put in the same amount of effort and are achieving the same results, then in the long run, it is the first group of people that will show greater improvement and find themselves climbing higher and attaining more in life. And all it takes is a shift in mindset.
Why you might ask? Coz from the time we were born, each and everyone of us, worked best and well with encouragement and support. Think of your friend's new born child or even yourself as a kid. The kind of environment that you were in was a very naturing environment. Each brand new step you took was marked with encouragement and praise. And that was probably how you learnt to speak and how you learnt to walk. And from walking, you learnt to run, to jump.
And that is why the people who are happier generally perform better then their peers who are unhappy. The unhappy group of people might find that the task is too uphill and give up. Or be constantly struggling with their inner emotions of not succeeding and losing focus on the goal that is in mind.
I haven't quite figured everything out just yet. Hoping to hear some response as to what you think is true or not? Does this argument hold true and is it valid?