Why good planning is useless without good controlling by managers?

Good planning is only the first stage of the project management process, and without proper and controlled execution, you could have the best plan in the world, but it would be utterly useless if you could not implement it. Many people concentrate on trying to get a well defined plan and then try to implement it, and develop the plan and then never look at it again and wonder why the project fails. The key is to have a strategic plan of where you need to aim for, be aware that plans change to deal with risks/changes and you will need to take advantage of opportunities, with a high granularity for the next few months that you are happy is achieveable, and then a longer term view at a higher granularity to the end of the project. As the project proceeds your high granularity window moves forward and you address the issues in a prioritised and staged manner. This allows managers to concentrate of the immediate issues, whilst making sure that their actions fall in line with the strategic end goals/objectives. Too many plans are the same granularity throughout the plan, and take too much effort to maintain, and that is why some managers neglect them. Remember that planning is just one of the tools in the project managers toolset (others include risk management, stakeholder management etc), and ultimately your plan must be resilient enough to survive anything that the project throws at it. Very rarely is anything delivered exactly to the original specification, so make sure your plans can accomodate change, otherwise you maybe trying to deliver something that will not meet your unwritten Customer requirements (e.g. fit for purpose, customer directed changes throughout the project) and you will not sign-off on. Constant re-planning is the method of getting from your start position to your end point, and constant control throughout the processes makes it happen.