This is a huge issue about making strategy stick, and it's no coincidence that the illustrations you've used are about people doing the wrong things, more than about them not doing the right things. So often we see strategies that set a new course, target a new market or chart some new territory, but don't tell people what not to do - and that is the strength of focus.
I have often run a simple exercise with teams at risk of falling into this trap. Take a large piece of butcher paper and draw a big red box in the middle to represent 'What we do do,' leaving the outside for 'What we don't do'. As the team suggests customers, products, services or activities that should be inside or outside of the box, the debates can be surprising. Identifying those things that are just outside or just inside the edge help to clarify your boundaries, and putting the page up on the wall can serve to maintain the focus.
Then the hard part starts - actually saying 'no'.
