Not sure I completely understand the question but, if you mean for example, I'm aiming for 8 curls but shit the bed 1/2 way through the 7th then no, I'll hang the bar up, call it a shit day/set, rest 30 seconds longer than normal (bout 90 rather than 60 sec) and start the next set, if I don't get the number of reps I aimed for in that set either, I'll focus on that body part / exercise as a priority next time it's due, normally 4 days.