Say I were exposed to someone who has the flu. And the chance of me getting sick were 50% from being exposed to that person. Now, say 50% of the people who actually have the flu virus develop symptoms within the first 2 days. I make it up to day 3 without any symptoms. I think I should be able to cut my odds again that I did not contract the flu from this person: 1/2*1/2=1/4 chance I may have the flu?