What do you know about how much you can get done in five minutes? For people who write all the time, five minutes is enough to write a paragraph or maybe two paragraphs. It's an opening to a conversation, an insight jotted down for more reflection, a quick answer to a quick question. For other people, five minutes is not enough to say anything finished, anything of worth. For those people, anything worth the effort of writing takes more than five minutes to consider and communicate.
Set a timer and write for five minutes on any topic that is currently engaging your attention - five minutes on next steps in a project at work, five minutes on what you would like to ask your child's math teacher, five minutes on what you want to accomplish before the end of the year. The only vital elements in this exercise are that you pick the topic and you write continuously for five minutes (type or write without stopping to ponder - keep the cursor or the pen moving by writing whatever comes to mind or by complaining that nothing comes to mind - just keep writing).
As I watch the clock, it has taken me five minutes to write the first two paragraphs. That was long enough to introduce the exercise and explain what to do. If I had been a little more focused, a little more into a peak performance state, I could have produced this final thought as well: what you can write in five continuous minutes tells you what is in your mind and how you feel about it. If the writing is confused, it's likely because your thoughts are confused. If it's clear, interesting and opens a great discussion, you're probably writing about something you know congruently enough that you can inspire others.
Use the five minute writing test (or be daring, and stretch to ten minutes) to find out what's really on your mind. It is what you think: it might not be what you expect.