Like every other skill, lateral thinking is a matter of practice and willingness to be open to multiple ideas without censoring or trying to reach a desired outcome immediately. If you have always painted with a particular brand of watercolor on a particular brand of paper, the tendency of human nature is to continue to do so. That's the philosophy behind, "If it ain't broke, don't fix it." Be safe, do what you know best, enjoy your expertise. There's absolutely nothing wrong with that route, but eventually many creative people find themselves feeling unstimulated and stale with creating in exactly the same way each time.
Creativity is as much about the engagement and delight of the process as it is having a successful, predictable outcome. If that same watercolorist chose to work on a different type of paper, work with different brushes or brand of paints, employ different painting techniques or investigate a totally new and intriguing subject, they would be certainly feel uncomfortable at times -- but also find a challenge in mixing things up that could add excitement and freshness to both their subject matter and methods.
There's an opposite type of artist though, one who tries so many different techniques and ideas that they never seem to be able to follow through on any one thing. A fellow artist I know loves the part of creating that involves generating new ideas. They have enough ideas to last for several centuries and never seem to tire of adding more to the pile. They're forever leaping excitedly into new techniques and whole new mediums on the wave of a new idea, then abandoning the one they've been on for the next big wave.
It's wonderful to have an open mind and think laterally. But out of all the possible, delicious ways we can express our artistic nature, out of all the visual stimulation that we find informing and fascinating, out of all the research and references we find stirring and inspiring in the creative works of others, eventually we have to choose one idea and focus on it.
In order to move from idea to actualization, we have to commit to working through the creative process. We have to take action and we have to complete what we start, because it is through that process that we learn and develop our artistic "muscle". This is the "sweat" equity that is built into creating art. Much like a musician or dancer, who practices a particular piece of music or a dance routine over and over before performing it, the visual artist spends a considerable amount of dedicated time in contemplating and then executing an idea for the creative cycle to come to completion.
Focus doesn't just mean working on one single project from beginning to end. Some artists are more comfortable having several works in progress at one time. But it does mean working to a resolution of that idea -- even if the ultimate resolution is to fail and learn from that failure how to improve the next time.
Actualizing ideas is essential to growing as an artist. People often ask me when I'm going to switch from working on the Pages and Parables pieces. Perhaps they are already bored with my exploration. But the fact is, the longer I stay with this series, the more I refine my own voice as an artist, the more I find the subject challenges and stretches me, and the more confident I feel in my own artistic voice and direction.
I don't necessarily attribute this just to working in a series. What I do attribute it to is my choice to generate options and generate new ideas and ALWAYS maintain my commitment and focus on following through to a resolution. I can, do and will continue to make some works that are more exciting than others, but each idea I manifest is the muscle I build as an artist, the strength that moves me forward and makes every step invaluable, from the excitement of beginning to the discipline and sometimes sheer fortitude of completing.