Pick Your Game Of Musical Chairs

The same number of people will be added to each game continuously.  There are a lot more chairs in the blue game than in the red.

The undertaker removes people who don't have chairs when the music stops.

Which game would you rather join?

This shows the flaw in using prevalence (the number of chairs) as the measure of a disease's impact.

The small number of ALS chairs doesn't mean that it's a small problem.  It means that it's a huge problem!