You know "the zone," the state of mind in which you're focusing on a task that is a good match for your abilities and makes time and self-consciousness melt away. We engineers have it, and I'm sure writers, musicians, and chefs do, too.
A key book in the field was written by researcher Mihaly Csikszentmihalyi, who (I'm pretty sure) came across the phenomenon of flow while researching the concept of "fun." A brief Wikipedia article outlines his theory.
In an article in Psychology Today, the researcher writes:
These exceptional moments are what I have called "flow" experiences. The metaphor of flow is one that many people have used to decribe the sense of effortless action they feel in moments that stand out as the best in their lives. Athletes refer to it as "being in the zone," religious mystics as being in "ecstasy," artists and musicians as "aesthetic rapture."
It is the full involvement of flow, rather than happiness, that makes for excellence in life. We can be happy experiencing the passive pleasure of a rested body, warm sunshine, or the contentment of a serene relationship, but this kind of happiness is dependent on favorable external circumstances. The happiness that follows flow is of our own making, and it leads to increasing complexity and growth in consciousness.
By the way, he found that basic leisure activities, such as watching television, often do not result in the "flow" state.
It's been far too long since I've experienced flow. My responsibility list has grown, and correspondingly my "incoming information world" has become uncomfortably high-bandwidth, broad, and shallow.