Isn't there an old English folktale or folksong with that title?
If there isn't, there should be.
Not that all luck runs downstream . . . .
The ebbs and flows,
The floods and shoals . . . .
I now tend to consider carrying such a luck piece a worthwhile wooing of Fortuna. This wrought clod-of-clay gives me something to turn in my hand -- a talisman, a worry-stone --for when I grasp at a bit of boost, that palpable push, from the web-footed luck of the big-billed duck.