* Management is always right.
This truism is built into the entire fabric of software development: whether your process is an agile one where the product manager has ultimate knowledge of what is needed and on what timescales; the project that is delayed not because of bad planning or poor company organisation but because the developers are not working hard enough; that the only variable that affects the business is how productive / expensive the developers are - all the factors that describe how effective the management is are completely ignored or irrelevant. The list goes on and on and described in better detail in all the comments here.
Of course the solution to all of this is better data. You can be sure that the volume of data is inversely proportional to the strength of belief of the above statement. This leads to the second fundamental mistake that management makes:
* Not reading High Output Management by Andy Grove.