What's to be confused about? When a male meets a female (let's say between the ages of 18 and 75) he immediately files her as a yes or a no. That assessment is affected by many things such as beauty, reputation, clothing etc and then by alcohol levels and abstinence periods. It is also possible for the file to be reassessed in the light of additional information.
For a one nighter, it never goes beyond that filing system. Where it gets more complicated is where there is no one nighter and more information is compiled prior to the decision of whether to make a move or not. The standard required to initiate the research operation has to be higher than the one nighter or we would all be so bogged down in research that one nighters would never happen.
See how simple that was. Keep it in your wallet because it will serve you well.