Mihaly Csikszentmihalyi, a professor and former chair of the Department of Psychology at the University of Chicago, pioneered the study of flow. He wrote that flow is the "holistic sensation that people feel when they act with total involvement." 
Csikszentmihalyi wanted to understand the experience of enjoyment. He asked, what motivates people to perform better? Extrinsic rewards like money and prestige are limited resources that ultimately are about comparisons between people. Status is a zero-sum game; so something else must motivate us humans . Intrinsic rewards, doing activities for the sheer joy of it, are the key to understanding flow. 
In order to understand intrinsic motivation, Csikszentmihalyi studied self- rewarding , or autotelic, activities. Csikszentmihalyi knew that if he could understand what made us tick, he could revolutionize how we work and play. He observed painters , rock climbers, dancers, musicians , and surgeons, taking surveys and later paging them at random intervals. His goal was to answer one of life's greatest questions: What makes life worth living?
The answer is that life is worth living when we can experience the joy of doing what we want to do, have autotelic experiences, or flow. Without flow "there would be little purpose in living." 
Flow is a positive, highly enjoyable state of consciousness that occurs when our perceived skills match the perceived challenges we are undertaking. When our goals are clear, our skills are up to the challenge, and feedback is immediate, we become involved in the activity.
We can become so involved that we lose our sense of self and time distorts. The experience becomes autotelic or intrinsically rewarding; we do it for its own sake. People who have experienced flow consistently report the same nine dimensions: 
Unambiguous and immediate feedback
Skills that just match challenges
Merging of action and awareness
Centering of attention on a limited stimulus field
A sense of potential control
A loss of self-consciousness
An altered sense of time
An autotelic experience
Flow depends on how we perceive our skills and the challenges at hand. We may feel "anxious one moment, bored the next , and in a state of flow immediately afterward." 
As you can imagine, as our skill level improves , we must undertake more difficult challenges to achieve a flow state. Flow encourages us to improve ourselves and our web sites. People tend to repeat activities they enjoy, so flow is like a Darwinian force of nature, subtly changing society.  That's why people tend to return to web sites they enjoy.  Csikszentmihalyi wrote this about flow and cultural evolution:
"Flow is a sense that humans have developed in order to recognize patterns of action that are worth preserving and transmitting over time." 
The best memes are passed down through generations.
Our supply of attention ( otherwise known as " bandwidth ") is limited. Csikszentmihalyi estimated that we can process about 126 bits per second, which I'll update in light of recent findings. This is based on our ability to recognize seven chunks of information per unit of time, plus or minus two, and Orme's estimate of our "attentional unit" of 1/18 th of a second.  This gives humans 18 x 7 or 126 bits per second of processing power.
As you learned in Chapter 1, "Response Time: Eight Seconds, Plus or Minus Two," our span of immediate memory is more on the order of five,  or as low as three,  which means that our bandwidth is on the order of 90 to 126 bits per second. That gives humans a processing power of around 5,400 to 7,560 bits of information per minute. 
What can we accomplish with this limited attention capacity? Csikszentmihalyi estimated that listening to a conversation takes about 40 bits per second, or about one third to one half of our bandwidth. That's why it is so difficult to listen to multiple conversations, or to play engrossing games or sports while listening to a conversation. It's also one reason why designers are told to minimize distractions on the web.