Thinking about it more, the most unrealistic part isn't just that you only care about the top 1. (Even if you were willing to accept top 2, top 3, etc, the decision rule would still be to reject the first X% of applicants).

Bigger culprits are:

• Caring only about ranking, and not the actual quality level. Most people would be perfectly happy to marry their first partner if the relationship quality is good enough, without worrying about whether there's a better match out there.
• Assuming you know N. One reason you should be happy to marry your first partner if the relationship is good enough is because you just don't know when another opportunity will come along.