According to a survey on classic mistakes in software development by Construx the Most Common Classic Mistake is “Overly optimistic schedules”, very closely followed by “Unrealistic expectations”.
In my experience both mistakes can really kill a project, and if the 500 people participated in the survey feel the same one wonders why these mistakes still take place on such a wide scale.
In my time as a project manager at a large telecommunications company I quickly learned the art of realistically estimating software projects after having falling flat out on my face once or twice.
One of the most common mistakes in estimating software projects is to rely blindly on an estimate of a software developer. Almost always they just tell you the time they believe they need for coding only, many times assuming you will add the time for preparation, testing, documenting etc. yourself. I know because I am also a software developer myself.
The most reliable method if you – as a project manager – need to come up with an estimate quickly is to follow the law of pi and multiply the programmer’s estimate by 3.14.
You will be amazed how many times this estimate will turn out to be very close to reality!
(Image copyright Gord Caulkins and used with permission)