Who are the customers you can’t afford to lose? Often they are those customers who produce most of your sales or most of your profit. I start with sales because this is the easiest place to look. Simply run a report of your sales for the last 3 years by customer. Ideally, sort the customers from biggest to smallest. In the 1980’s people talked about the 80/20 rule, 80% of your business came from 20% of your customers. Today we often see the 95/5 rule, for many companies 95% of their business comes from just 5% of their customers.