According to positive psychology research, yes you can and it is easier than you think!
It has been found that if you wake up every morning and practice saying three things you are grateful for (or happy about!) and they have to be new each day – by doing this for 21 days, even people who were testing as the low-level pessimist on average were now testing as low level optimist. Now that doesn’t sound that huge, but here’s the amazing thing. We can do this with an 84 year old man with genes for pessimism…if you do this for 21 days, what we find is that even if you’ve practiced pessimism for eight decades of your life, even if you were born with genes for pessimism, when people practiced this, I would never guess before this research that literally two minutes could trump your genes and your environment. – Shawn Achor Havard University Happiness Researcher
You might have heard of the term neuroplasticity – this means that our brains are not fixed, but rather are constantly changing and evolving based on the information being wired from our thoughts and experiences. The brain wires in whatever input appears and does not differentiate between positive and negative. Over time patterns form which can create biases – eg we often develop a negative bias after having a lot of stress or a few weeks of things going wrong so that our brain starts to anticipate and code events as matching – even neutral information can be coded as negative once we are stuck on this pathway and our brain can start to not even notice the things that are positive or that contradict this. It is as though the negative sticks like velcro but the positive slides off like a teflon pan!
The exciting thing is that the same dynamic works for positive encoding so that what we attend to, is what our brain wires and seeks more of. Perhaps try an experiment for one week by writing three things you are happy about or appreciative for (different things each time and they can be the tiniest things) in a notebook or even on your phone. Writing it down is important because that helps your brain to encode this (or velcro it in) more deeply.