There are many frameworks on how we make decisions. Personally I like to keep things simple so I can remember the entire process. The framework I suggest has three outcomes: Deterministic, Probabilistic, and Heuristic.
Deterministic, is when the outcome is easy to spot and it shows itself clearly to you. As an example, if you want to drive from home to your office and you must do fast, then follow the shorter rout to your office. You did it before and you do not have time to experiment a new rout.
Probabilistic, is when we can decompose the problem in smaller components and measure the probabilities of success or failure. For example, you want to start a new project and you measure the Net Present Value (NPV) of the project. As you already know, if the NPV is more than zero the venture is profitable. If it is below zero you will reject the project.
Heuristic is when it is not deterministic and not probabilistic. It is not possible to decompose the problem because the complexity. In this case use your best guess, something worked before for you in the same or similar situation. An example is Pareto theory. Pareto states that 20% of your customers produce 80% of your profit. We do not have a scientific evidence of so but we know it is the truth!