As humans cannot know everything, so they rely on educated guesses, that could be referred as probability, via deploying confidence interval for mean and proportion, statistical community attempts to fabricate a bracket of numeric values, that might contain the desired parameter with usually 99%,98% and 95% probability.

The examples confidence interval for mean could be, if someone wants to estimate the average population of a forest in different time periods or a doctor interested in quantifying the average number of people dying from a particular disease. The example of proportion could be taken as the number of voters, opting for a peculiar candidate in the elections.

The Use of Confidence or Fiducial Limits