Communication during change - what should you focus on?

Communication during change - does anyone get it right? This research shows there is still a long way to go. Read the useful comment at end.

Communicating the 'why' and the 'how' are the most significant drivers.

But you can only do this well if you have  complete clarity on the 'why' and 'how' yourself.

In my experience many change managers aren't clear on this. How can you be a change leader without it?