What is the origin of the word "chicken-shit" to describe someone who is unreasonably afraid?

I don’t hear it much anymore except from my friends, who like me, heard it from our fathers.

Example-I have a vivid memory of a tournament little league baseball game and letting an absolute meatball go by me, and getting a called strike and an out and game over.
After the game, my dad (smiling, by the way) sort of patted me on the shoulder and said Nice swing, chicken-shit

Another example- I was a little kid and part of passing my next level at swimming lessons was diving off the high dive. I sort of hesitated at the bottom of the ladder and the instructor, said You can do it. Don’t be a chicken shit. Not malicious or threatening, just chicken shit.

My friends say it all the time on the golf course.
Today, for some reason, I can’t get it out of my mind. It’s actually sort of funny simply to say.