If you’re trying to make a decision under uncertainty, the most important question often goes unasked: is it worth investing in learning before making my choice?
Combining two other tools from this site and an idea from reliability engineering, we can create an engineering model of which uncertainty to prioritize.
Suppose we have several sources of uncertainty. For each one, you can also choose to reduce your uncertainty by learning.

Next, we look at how the uncertainty impacts your decisions. We start to see that some uncertainties will be cheaper to reduce, while also having a bigger impact on our decision depending on the unknown.

However, decisions and uncertainties don’t happen in a vacuum. While in this illustration there are 5 separate sources of uncertainty, we’re often making a single decision. In reliability engineering you can connect these subsystems and see how the overall system behaves. Sometimes the uncertainties and decisions stack up, like a chain. In those cases, you look for the “weakest link” to see where to focus your learning.

Other times, learning about the unknown could set you down a different path. In reliability engineering Figure 4 shows a top path where unknowns 2 and 3 are said to be “in parallel” compared to unknowns 4 and 5.

This provides a model for seeing which uncertainty to prioritize reducing in order to make the best decision possible.