"The Flinch" by Julien Smith
It's free. (You can download both the book and - if you don't have a Kindle - a program to read it on your computer at Amazon.)
It's very short. (There's a lot of advertising material for other books attached at the end, though.)
It's about flinching from frightening task - but that was already obvious to you, wasn't it?
... and for all those reasons, I won't write anything more about it, because it'll probably be faster if you just skim it.