I've been guilty of the continual thing in the past. But although I do see the LD side of it, I'm not sure you see the HD side yet.
Rather than looking at percentages, like the one in twenty, how about looking at frequency. Let's say that your S was willing, on the average, once every six weeks. It's not every six weeks, but an average of every six weeks. It might be six weeks, but it might just as well be twice in one week, but then nothing for another twelve weeks. Then let's complicate it a little further by throwing in the fact that your S won't tell you when those times are and won't initiate. And yes, I did live with this.
So as the HD, what do you do? Knowing that you'll only be successful and average of once every six weeks, do you only try once every six weeks? In that case, you'll only have a one in forty-two chance of hitting the right day to try. Every three weeks improves your odds of hitting "the" day to one in twenty-one. Once a week ups it to one in seven. Every other day makes it one in two, and every days makes it a certainty.
BUT, what I've left out of the equation is that the more you try, the more your S gets irritated and the less likely your S is to do it. So the very thing that increases your chances of trying on that magical day when your S is willing, also has the side effect of increasing the chances that your S will be too irritated with you to do it anyway. So it ends up looking like a lose-lose proposition. If you don't try, you'll miss the opportunity. But if you do try, you'll piss them off and there won't be an opportunity to miss.
Such is the HD conundrum. And I would venture a guess that a lot of HDs opt to risk irritating their S rather than risk missing one of those golden days when all the planets align and when they actually have a chance.
