But, few professional writers actually spend all their time writing – instead they get a few words or paragraphs down, take a break or write about something else, then return to the initial project. And, they may spend their whole day working this way.
And here's where you can learn from professional writers. Don't try to get all of your message written at once – especially if it's an important message. Instead, think of writing as a series of intense moments broken up by longer periods spent doing something else.
For example, if you need to write an important memo, think about the chunks involved in creating it. Let's say your memo will start with an objective, in which you outline the problem that needs to be addressed. In the second section you outline the options for addressing the problem. Then, you identify and explain the solution you've chosen, and in the fourth section you list the benefits that should flow out of implementation of the solution.
That's a big bag of ideas to deal with all at once. Perhaps you might start with a simple outline and a few bullet points in each section. After that, you turn to something else for an hour or two before writing the first section. Follow that with a break in which you do something else, then you write the second section. Follow that same write-break-write-break process until you've finished the memo.
In summary, taking a bit-by-bit approach means you'll probably end up with a better message, one that's more likely to get the results you want.