How can leaders chart a course when they cannot predict the outcomes of their choices?

Much of the time you can see what the possible outcomes might be, and assign a probability to each one.  You can affect this probabilities by planning and preparation.

There is always uncertainty in the future.  That uncertainty does not, in general, favour any one outcome over any other.  This means that sometimes you can simply ignore the uncertainty - it affects all the possible outcomes equally.

Sometimes of course, you just have to take a deep breath and decide.  In such cases you remember that the wrong plan executed well is still better than the right plan messed up.