It's down to trust.
Somewhere along the line you have to trust both people and the physical world around you. As for myself, I know air is pretty thick and that a wing will produce lift. I trust work of the designer and the manufacturer and accept that they have done their jobs properly. I also accept that the certification system will not pass any contraption that is capable of being flown and operated by someone verging on to be a complete idiot. I also accept that there is the possibility of something going wrong in any one of the previous items. When I'm learning I also try my very best to understand what I'm being taught and why. As a direct consequence of all of the previous items I'm a happy bunny when I'm in a plane.