For those born in or dragged in as little children, normal customs are not imprinted on our minds.
Such as the simple saying ''bless you'' when somebody sneezes. This has frustrated my wife for as long as we have been together! She felt it very rude that when she would sneeze i would not respond with the customary phrase, I had to explain that it just was not part of my culture, not imprinted on me. It is like expecting an african bushman to offer the exchange.
Its not like i heard the sneeze and thought 'bless you', then had an aversion to saying it, it just never entered my head in the first place...this did satisfy her but she still wanted it none the less.
So i been learning! And I do now actually think: Aha! A sneeze! I am to say something! Ah yes, "BLESS YOU"!!!!
one day i am sure it will be automatic.