From my experience, PU is like a performance which requires energy and effort. You are supposed to entertain your target which is hard if you are tired.

I have realized that everything about PU (or rather seduction actually, since it is possible to pick someone up without seducing her first) boils down to one thing - attention. You need to make your target pay attention to you for quite some time (a couple of hours). This in turn requires that you can lead the conversation, have interesting things to say, be fun and stimulating etc. You can do this if you are tired too, just not as easy.

To answer your question... Do you call it a night or do you break out of it? It depends on how desperately you need results. I would rather call it a night and try my luck another time. As with desperation in general, it usually spoils everything anyway, in one way or the other.