Like pricing, estimation of time and effort can make or break any project. Here too, often estimates are manipulated in order to secure orders. Time estimates have to be calculated based on practical considerations such as unplanned events and reduced productivity if employees work tight schedules or are not adequately prepared.cutting corners can also reduce productivity and increase timeliness. The biggest and most common mistake is thinking people can be uniformly productive and available all the time. Humans tend to have good and bad days and productivity varies. People tend to get tired , fall sick and have personal commitments . People get married too and may even simply want to take a day off or a vacation and these cannot be denied. While planning for resources, these must be taken into consideration. Employee churn is a critical and realistic factor and must be considered . One cannot wish it away and mishandling it can demotivate or demoralize employees and replacing an employee can be very expensive in terms of time too.