The zone system rule in a nutshell is (as mentioned) "expose for the shadows, develop for the hilights".(posted 9406 days ago)The _reason_ for this is (with negative film) you don't want to underexpose, and you don't want to overdevelop. So if you've added exposure to get shadow detail, if the hilights are very bright, you need to reduce development to not overdevelop those areas and block up all off the hilight areas.
These are the ideas behind the zone system. Now you can pile on all of the calibration and testing to very precisely set your film speeds and development times...