why the more slack you are, the more emergency fund you need

This is prior to http://small-timeinvestor.blogspot.com/2020/05/true-meaning-of-emergency-fund.html

There are two points to see this :

1) Work performance

This is rather straight forward. Your work performance may be deemed as "slack" by your superior for various reasons. Thus your "slack" work performance will require you to have some short of buffer in terms of savings, in case shit happens.

2) You want a "slack" life

This will define the quality of "slack" life. Some are good to go for 3 simple meals, while some want daily posh meals. If you are the second type, prepare to grind more hard and also save more, in case, the first point happens.