How long do you give a ‘project manager’?

“When asked at which point a club gives up on a ‘project’, a mixture of current and former directors at Premier League clubs tend to arrive at the same answer. ‘When the fans say so,’ says one of them, who would like to remain nameless because he does not really want to admit publicly that, in the past, he has helped pull the trigger because of the pressure he and his colleagues were under. …”
The Athletic