I think you are confusing a few things. First, yes, if you want to figure out your chance of dying from doing two things, you would have to do the math as you

I think you are confusing a few things. First, yes, if you want to figure out your chance of dying from doing two things, you would have to do the math as you describe. You’re Russian roulette example isn’t a problem with the units. The chance of the bullet firing is not constant in each round, which is why the odds work as you describe. Each round has a different micromort number. The point of a micromort is to compare activities for risk, not to calculate the total chance of dying after some series of activities. That would be impossible anyway; there are infinite activities you go through, each with their own micromort level.