You might think that all swans are white because you have never seen a black one. But there are black swans, in Australia. Karl Popper, a famous philosopher, held that even the so-called laws of science are hypothetical, subject to being disproved someday by new evidence. You only need one counterexample to disprove a claim of “never” or “always.” All swans are white — until you see a black one. But you can never tell when that will happen.Perfect knowledge is seldom if ever available to humans. For one thing, new information is constantly arriving, and human learning is constantly expanding.
While we can’t be absolutely certain, we can be certain enough to make a reasonable decision.
In the U.S. court system there are various standards of certainty. A criminal trial requires a much higher level of certainty than a civil trial to convict a person. (Consequently, an individual may be found not guilty in a criminal trial and guilty in a civil trial, e.g. O. J. Simpson).
In our everyday lives, we have to pick an appropriate standard of certainty. With trivial matters the level of certainty can be low, but for nonreversible decisions such as when choosing a spouse or a president, a much higher level of certainty is required.
Be as certain as you need to be.
— Unspun by Brooks Jackson and Kathleen Hall Jamieson