Three is the magic number

Everybody knows that in writing three makes it easier to remember and tell a message. Some people would also be aware that, in mathematics, the rule of three is another name for the cross-multiplication which applies to the equation between 2 fractions. But only a happy few would know that strategy has also its rule of three (or four).

Two professors wrote a book "The Rule of Three: Why Only Three Major Competitors Will Survive in Any Market" about this simple and realistic dogma. The rule states that in any industry, in the long-term, there will only be 3 or 4 major competitors and a long tail of niche players. Examples can be found in many mature industries and experience has proved that rule true.

• UK supermarkets: Tesco, Sainsbury, Asda
• PC manufacturer: Dell, Lenovo, HP, Acer represent more than 60% of sales, the 5th one is Asus with 5% only
• Sport shoes: Nike, Addidas, Reebok, New Balance
• Game consoles: Nintendo, Sony playstation, Microsoft
• Online shopping: Ebay, Amazon, Alibaba
• UK Retail bank: Lloyds, RBS-Natwest, HSBC, Barclays 

More examples can be found across the world. Fundamentally, in any industry, in the long term, there will only remains three! Would this be applicable to any other areas such as geopolitics or your own social groups?...