When a doctor announces that his treatment has 75% chance of being effective, what is he doing? Setting expectation based upon past experience/empirical evidence. There is no law involved here, no science (knowing), just personal/professional experience.

We have a choice, although few choose... either everything is chance or there is no chance. Either existence is made up of good luck and bad luck, or there is no such thing as luck. If chance or luck is legitimate, then we are doomed to amoral non-intelligence, for that is what luck is.