Product Vision vs. Mission
This post is basically a pointer to the Product Vision vs. Mission page. To use the same quote as the page.
If you want to build a ship, don't drum up the men to gather wood, divide the work, and give orders. Instead, teach them to yearn for the vast and endless sea.
In the page author, Marty Cagan, explains the difference between product vision and mission statement. To quote;
Most people I meet, when they show me their "product vision", what they are really showing me is their "mission statement". They are confusing a slogan about their purpose, with a product vision.
It may be useful to revisit this page whenever starting a new project to formulate those two.