Due to the ongoing problems with the missing contents this is just a short one. Plus I haven’t done one of these for a while.

Why should something be a shoe-in? What on Earth can the phrase have to do with footwear?

OK; I agree shoe is spelled the way shoo sounds. But why would you use one to usher in a dead cert? Unless you’re confusing it with to shoehorn. But that means the opposite of certain. You only use a shoehorn when you’re having difficulty getting a shoe on your foot. If it slips on there’s no need for a horn.

I’ve always thought of this as a shoo-in, as in shooing something away.

It seems it’s actually derived form horse-racing, from a “fixed” race where you only had to “shoo” the intended race winner over the line.

Much as I thought.