>If it stays constant (flat), then the total number of cases will increase in a straight line. What? After a set period of time, active cases become past cases

>If it stays constant (flat), then the total number of cases will increase in a straight line. What? After a set period of time, active cases become past cases. People recover (or die). If the number of new cases per day is flat, than the total number of active cases will also become flat (after a delay if it was growing previously). If the number of new cases per day declines, the number of active cases will also decline (all the way down to zero as you say if the number of new cases drops to zero). I am genuinely confused by what you're writing here. "Number of new cases per day" isn't the same thing as an increasing rate of new cases per day.