We're a little off tkamiya's original topic which was more about how we perceive print values in the context of an image. But to address the evaluation of prints as raised by Brian, I'd offer the following.
Regularity counts for a lot when judging your prints during a printing session, because prints can often look so different under different lighting etc. It's not enough to have excellent technique. Because I don't get to print every day (and there can sometimes be periods of weeks or even months of no printing), I don't make final decisions in a single session. I stop when I think I've got it pretty much right, make a few versions, wash, dry and then live with them for a while. If I don't do that, I find myself spending too much time staring at my microwaved work prints, moving from room to room to look at them under different light levels etc.
Refraining from final decisions in a single printing session is particularly helpful with complicated, labourious prints, in which case by the end of a printing session I'm sometimes too immersed in the complexity to make an ideal overall evaluation. Sometimes even coming back the next day makes a difference. Things that aren't quite right will tend to jump out at you more easily. Or sometimes I'll realize the print is just too dark, contrast needs adjustment etc. It's a chance to really evaluate the direction you took and whether or not the original desired outcome has been realized.
I've also found this technique makes my printing sessions more fun because my stress level is lower if I know I don't have to have it all perfect by the end of the session. Otherwise I tend to get pretty stressed out when printing.