The Three Four Rule

Bruce Henderson the legendary founder of BCG came up with this wonderful rule based on empirical data.

Three Four Rule - For any product there can be only three major competitors in any market.
Also the market share of the largest firm can not be more than four times the share of smallest firm. Or if interpreted in a different way, a firm cannot compete effectively if it's market share is less than the quarter of market leader's share.

A very interesting thought indeed.

cheers