The critical few are the minority of causes that contribute to the majority of the effects. The critical few is the ‘20’ part of the Pareto Principle, otherwise known as the 80-20 rule.
Addressing the critical few has the potential to provide the biggest bang for the buck. In most cases, you can conserve your continuous improvement resources by concentrating them on the critical few.
One word of caution when using the critical few to address problems in Lean. The term is not always analogous to the ‘easy few’. Just because the critical few contribute to the bulk of the effects doesn’t always mean that they are the ones you should go after immediately. You may find some low hanging fruit in the trivial many.