Without a doubt there are some people 'on the street' who can be
trained as pilots, but the prudent move would be to choose candidates
from an enriched population. Of course it means there are some really
potentially good candidates who would therefore not get selected, but
the wise manager will do everything she can to choose well.
Interviewing a thousand off the street to find a 'keeper' is a lot
less efficient than choosing someone from a target rich environment.

This is not theory, but real life stuff.