How many attempts does it take?

In the current class I'm taking on drawing faces, we draw A LOT of faces.  The goal is to draw 101 faces by the end of the week! In most assignments, we make between 8 and 10 from a particular technique.  Which seems like a lot, except out of those 8-10, I will usually only get 3-5 which I actually like.  One of yesterday's assignment was to draw faces using a ink dropper. I used a Distress Reinker (Vintage photo) to draw a variety of faces.  I liked these three, but my other seven attempts will never reach the light of day or, I suppose I should say, the light of the blogosphere. In fact, at the end of class, I will throw them away (as well as my other failed attempts from various assignments). 
Which got me to thinking about how many attempts at something it takes to create a "keeper." With the advent of digital photography, it's easy to take lots of attempts and delete the bad ones.  I think I probably delete between 1/3 and 1/2 of the pictures I initially take. I don't think the question comes up in other paper crafting fields (I don't usually throw away cards or layouts, for instance). For my art journal pages, I don't throw away the ones I hate. I either gesso over them to start again or simply turn the page and try not to worry about it.  On the other hand, I do have some mixed media canvases which I tossed (or gesso'd over) because they were, well, bad. LOL! What about you? How many attempts at a project does it take you before you create a keeper?