Ask HN: How to pick between 2 amazing ideas?

Let’s say you’ve got two really, really great ideas. I know that “ideas don’t matter” and that “your idea might not be as good as you think it is,” but, for the sake of this thought experiment, assume the opposite is true. Both ideas are amazing and will change the world in mind-boggling ways. More importantly, you are completely capable of executing on both of them, and neither is super complex or overly difficult; it’s merely a question of which to work on.

How do you pick one? Or, preferably, how do you (successfully) start both simultaneously? Is it possible?

Seeing that many startups are bootstrapped, also assume that you have to work on the startup(s) alone or with a small team until launch and for at least 3 months afterword. IE, you can’t hire a bunch of people to do the work for you, at least at the beginning.

Some possible lines of thought:

  Which has a bigger market? Which will impact more people? 
  Which will make more money?