My favourite answer …

Everyone claims to “hire only the top 1 percentile”. If that were true, 100% of employed people would all be in the “top 1 percentile” of all people, so 99% of all people would be unemployed (in any given field). As this is clearly not the case, and we’ve all experienced people who’re clearly not in that group (why else do you ask this question at all…) we know this isn’t true.

In fact organisations made up solely of such people would be highly unstable. Too much ego, too many conflicting ideas. It’d either fall apart as everyone does his own thing, bog down in never ending theoretical discussions about the relative merits of everything, or evolve into a constant shouting match as sentiments flare whenever a decision has to be made.