Decide with information I do not have

When the missing information may never arrive and the decision still has to be made.

I am missing information. Help me decide without it.

1. List what I do not know, and split it: knowable with effort, knowable only with time, and unknowable in principle.
2. For the knowable ones, say what each would cost to find out and whether it would actually change the decision. Most would not, and that is the point.
3. For the unknowable ones, which option is most robust across the plausible range of values? I want the choice that is acceptable under most outcomes, not the one that is best under the most likely one.
4. What is my exposure if the worst plausible case is true? Can I cap it?
5. Recommend an option and say what you would watch for to know early that it is going wrong.

The decision and what I do not know:

Deciding under pressure. Making the call when time is short, information is missing, or your capacity is already full.