Probably similar to that "bitterness" test that a lot of kids got to do in science class where you taste that little strip of paper. To some it's nothing, to others it's very bitter. Genetics has given some the extra "taste", supposedly that might allow people to avoid eating poisonous things containing oxalates or glucosinates. Unfortunately it also means you probably dislike things lie IPA beers or other foods that have bitter compounds that don't bother others.