20% of issues should command 80% of the focus of a campaign and policy. 

20% of engaged voters need the tools and information to influence the 80% who will decide on the day. 

20% issues (think things like trans or Medicaid in the US) need 80% of the thinking to formulate policy positions that are electable. And should be very carefully handled. 

This is all focus group, polling and strategy stuff. And it is usually different locally, regionally and nationally with differences between gender, past voting behavior and wealth/education/income levels. 

It’s foundational to being an electable candidate party.