Strategic focus really does pay off: https://goo.gl/vKr2V1
As well as saying 'no', be prepared to say 'stop' - strategy needs to be agile and, as circumstances change, it may be necessary to go in a new direction to achieve the vision. Too many persevere beyond the point where it is commendable to do so, when it is clear that the benefits initially identified will not be achieved. Reasons vary but include fear of being seen to fail, emotional attachment to a particular programme or project and desire to justify expenditure to date.