Risk or Uncertainty
I guess most people think risk means uncertainty; “if you are not certain about something you are taking a risk”. Interestingly, by definition, risk is different from uncertainty: Risk means there are some “known unknown” that you know those known issues might happen, but you don’t know when it will happen, in what direction, and to what extent.You can think of interest rate as an example.
Uncertainty means there are some “Unknown Unknown” that you don’t know what might happen at all, and obviously the direction and extend is unknown as well. 9/11 can be considered as an example.
So, the difference between risk and uncertainty is that risk is a probability that can be measured (or calculated); for example the chance of having an interest rate less than x in next year can be calculated.
How about certainties? Means things that we know will happen for100% ? It seems there is only two things that we will happen for sure: tax and death! Let me know if you can name anything else!