The best quitting criteria combine two things: a state and a date. A state is just what it sounds like, an objective, measurable condition you or your project is in, a benchmark that you have hit or missed. A date is the when. Kill criteria, generally, include both states and dates, in the form of “If I am (or am not) in a particular state at a particular date or at a particular time, then I have to quit.” Or “If I haven’t done X by Y (time), I’ll quit.” Or “If I haven’t achieved X by the time I’ve spent Y (amount in money, effort, time, or other resources), I should quit.”
Annie Duke in Quit