(#1 in what might or might not be a series)
We’ll cross that bridge when we come to it.
How could you cross a bridge before you’re at the bridge anyway?
Or was it that there was a war in the 1700s and some soldier was worrying about a bridge being slippery and annoying the general. Would he reply “We’ll cross that bridge when we come to it. Don’t worry about the bridge for now?”