Chris Anderson

Long tail - forces:

1. More stuff is being produced. Technology and the internet make it cheaper and easier to record and distribute your own songs, publish your own writings and so on. This lengthens the tail.
2. There is better access to niches, again thanks to the reach and economies on the net. This fattens the tail.
3. Search and recommendations connect supply and demand. This drives business from hits to niches.

Long tail - conditions:

1. Variety (there are many different sorts of things)
2. Inequality (some have more of some quality than others)
3. Network effects (e.g., word of mouth and reputation, which tend to amplify differences in quality)