We set off the smaller rocket.
Our direction changes very slightly. But it isn't enough!
Our calculations show that we will get closer to the moon, but not close enough to land. Instead we will almost be pulled into orbit, but then continue our journey back the way we came, and head back to Earth!
We won't land, but at least we might survive.
Should we try again and risk firing the larger rocket? But using both rockets makes us more likely to hit the moon at the wrong angle: can we risk it? Or should we make the best of what we have, and study the moon from our half-orbit? Or should we do something else?