Comment by maxbond

No, you should definitely exercise good judgement in delivering a good UI to the user that doesn't lock up if they happen to type very quickly. But it is context dependent, and sometimes you will want to show them results for "a", sure. "No one" was rhetorical.

In your example, the developers have exercised poor judgment by making a brittle assumption about the data. That's bad. But there is no UX without some model of the user. Making assumptions about user's rate of perception is much safer (in a web app context, it would be a different story in a competitive esports game).