How Far Down the Road are You Looking?

When planning to launch a business or creative/artistic venture, there are two schools of thought.  The first is you need to make long term plans, look far down the road and prepare for what might or might not come your way.  The second is that you should just "launch" and let your plans develop around you.
There is merit in both but experience shows that a middle road might be best.
For example I know of situations where someone was wanting to launch a small one person business, but it never made it off the ground because he kept on planning and looking ahead 10 years and forecasting around every conceivable event.  This is the extreme of looking too far ahead.  On the other hand preparation to a certain degree can help ensure you survive some hiccups, however trying to plan for every event for a small niche business or venture is counterproductive.
If I was going to err on one side or the other I would rather err in launching without all the preparation and planning, at least then I would have done something which is far better than having volumes of plans and written goals but never even getting your feet a little wet.