A lot of people just don't have a clue what keeps an aeroplane in the air, so they are very stressed at the prospect of flying, as it is akin to giving control of their life to a magician . This probably accounts for some of the aggressive, out of character behaviour seen at airports and in airliners from normally rational people.
In the case of people you have known a long time, sometimes it is their having to adjust to you having acquired a new skill, and for some strange reason they would rather trust someone they have only just met to fly them, because he has been a pilot all the time they've known them, rather than the (now grown up) kid next door, who they remember falling off his tricycle, but is now a pilot.