I have managed many projects and hit deadlines and delivered to budget. The principles are simple: I would create a project plan with a granularity of 2-3 man

I have managed many projects and hit deadlines and delivered to budget. The principles are simple: I would create a project plan with a granularity of 2-3 man weeks per task. I would then go and discuss the plan with the team leaders and refine the plan to the 3-5 man day task level with their input. Given the available resources I would then add 20% and come up with a target date based on a realistic starting date. There is one very important distinction. When the requirements are unclear or non-existent, then the project could only be for the creation of the missing specification and repeat the process once the specification was signed off. As you may guess I have had many board level meetings where the stakeholders were horrified at how long things would take. That's where the politics start. Typically somebody pulled a deadline and budget out of their a* and demanded that I make it happen. That's where being a professional is very important. They either meet my demands or I decline the project. For example, in one situation I declined a project. They brought in a succession of 5 project managers and then axed the project years late and millions over budget. If it is impossible, then no amount of table banging and shouting is going to repeal the laws of physics, etc. You only need to read up on failed projects, like the FBI's Virtual Case File System (great write up in IEEE Spectrum), to realise that projects failing to meet deadlines are typically a result of management incompetence and rarely due to failing by the technical team - but that too does happen, especially if the specs are too loose and the team leaders fail to maintain focus.