When is a dirk appropriate?

[St. Amish]

Before strapping on a dirk with one's tweeds, I suppose one might ask the question, "What am I apt to be doing today that might require I have a stout 18-inch dagger at my side?" If the answer doesn't immediately pop into one's mind, then I suppose it might be a good idea to forgo the theatricality of the thing and leave the dirk at home on the sideboard, next to the ram's head snuff mull.

If that's the rule, then the sgian dubh is out, too, because I rarely have occasion to draw a 4 inch knife with a dull, ornamental blade whilst kilted.