We must learn to use our thinking mechanism to better supervise our moods.
We tend to look at our current circumstances and allow them to dictate our mood. And yet we have the ability to CHOOSE what we pay attention to.
So while we are generally not able to decide what mood we will be in - what emotion we will feel right now - we CAN choose what to concentrate upon. And whatever we choose to concentrate upon will affect our mood because we inevitably hold beliefs with regard to the object of our concentration.
If our priority is to maintain a good mood, we must be flexible enough to move our attention away from any thought or outside circumstance that feels unpleasant. Without that flexibility of attention, one is stuck paying attention to whatever thought or event is currently taking place - regardless of how it feels.
The intention to focus only on pleasant thoughts and circumstances must be coupled with a flexibility of attention for that intention to manifest as experience.
I have found, through my experience, that having the flexibility to move my attention AWAY from unpleasant thoughts and TOWARD pleasant ones is my/our single most difficult challenge.
My analytical and egocentric mind has always, throughout my life, dwelled endlessly on my perceived shortcomings, failures, and lacks. I see now that because I was expressing and focusing upon such limiting beliefs about myself, I was encountering them in my experiences - those beliefs were translated into my actual experience (that Reality 101, folks!).
In some ways, it is quite amazing that I have gotten to where I am now given my propensity for feeling sorry for myself and for thinking myself to death.
And yet now, as I apprehend how all of this works, I can see clearly how I have consistently allowed my circumstances and my beliefs about myself to dictate where my attention is. And as I take the wheel of my attention and learn to steer it deliberately toward pleasant thoughts and ideas and circumstances, it is a pleasure beyond words to begin to see the new and affirming beliefs I am choosing to focus upon being translated into my current and future circumstances.
And, I might add, I am indebted to more than a few teachers for such progress...