I don't get it. How does a 72 hour quarantine help anything?

Wait to find out if the have symptoms?

An unreliable, but easy way.

so flattening the curve i understand. is it possible to tell how far we need to flatten it? i've seen the curve skyrocketing upwards but is it possible to overlay that curve onto the flattened curve?

The easy part of the math is this:

maximum allowed curve size: new infected * rate of people needing emergency care * rate of emergency beds getting free

Let's say you have 7000 beds (respirators or whatever the critical equipment is).

A patient stays 7 days on average. Means you get 1000 free beds per day.

5% of infected need a hospitel bed. That leaves you with a care capacity of 1000 / 5% = 20'000 newly infected per day.

The other half of the equation:

If nothing is done, infections double approximately every 3 days. So if you have 1000 newly infected today, it will be 2000 in 3 days. 4000 in 6 days, 8000 in 9 days, 16000 in 12 days and in two weeks you are screwed.

The shockingly simple math of early retirement, but in this case the unwanted eternal one. (sorry, a bit of gallows humor here)