In any 'normal' situation it is found that approximately 20% of items account for 80% of the effect. The 80/20 rule. EG With 100 products there are likely to be 20 best selling products which account for 80% of the profit. Also there will be about 20 products (not necessarily the same 20) which account for about 80% of the profit. 20 of the products will account for about 80% of the customer complaints.