At the start of a typical project tasks are written down and estimated. Then put into a nifty tool where they are arranged before a reassuring (Gantt) diagram is produced.
Such a plan is a snapshot in time and represents an ideal world where things go according to plan. As the project progresses the actual status of the project steadily moves away from the status shown on the plan.
This mismatch is real and only natural. The problem is the plan, it’s still in peoples heads and starts to warp their perception of the project.
Which makes it easier to cling onto wishful thinking that there is still a chance that it turns out as initially planned even though the facts say something different.
There are cases where it’s clear that things are going off the rails and still nobody tries to adapt to reality. To some extent the initial plan is to blame for that. It makes people believe that things are still going according to plan to some degree and that there is still hope.
Instead a honest project management software should require an update each interval where target and actual status are compared. This makes people see the discrepancy and increases chances that the plan is adapted to reality.