It can be a matter of one fear being greater than another.
I have always been utterly terrified if heights - standing on a chair to change a lightbulb sort of height. When I was in the Air Force one of the radars I had to work on was a Type 54, an old metric radar mounted on a 300' tower. One day the transmitter tripped out and I was not quick enough to get out of the way, so I was tasked to fix it. Now one doesn't say to a Flight Sergeant "sorry chief I'm frightened of heights", my fear of the consequencies of that was greater so up I went. The trip up in the open lift inside the open tower was agonising, but at least the transmitter room was closed so I could work OK. When it came to getting down however, the lift had gone back down and there was no-one to answer my frantic rings on the bell, so I had to climb down the ladder on the outside of the tower, focussing firmly on the rung in front of my nose and nothing else, trembling, sweating and nearly in tears with terror.
After that you'd think I could say to myself "if I can do that I can do anything" - but no, I still feel unhappy clinbing on a wing to enter a DA40.
I know its all in the mind, but it doesn't help!