Not based off logic, but more so intuition and experience. Its a guess that is based off factors. For example, if you were to find the subjective probability that you were to buy new shoes with the same size as the current ones, the factors for this could be:
- Your gender. girls stop growing earlier than boys
- Your race. some races are short
- Your age. if you are old, then you will probably not grow any further
- Your budget. don’t buy anything expensive