(This is number 3 on my list of top 10 startup mistakes.)

I don’t refer here to the full formal business plan document that many startups need; I’m referring to planning, which all startups need. Set your long-term goals, your priorities and the meaningful milestones you’ll need to hit along the way.

Don’t ever confuse the plan with the plan document output. Don’t ever think the plan will last, or will be correct. The plan will be wrong, but the process of setting it up and tracking results will help you steer and manage your startup.

Never do something just because it’s in the plan. But never fail to plan. Plan right, understanding that it’s the planning process that runs your company, not the static plan document. Plan to change the plan often, as assumptions change.

All business plans are wrong–but vital.

Tim BerryTim Berry

Tim Berry is the founder and chairman of Palo Alto Software and Bplans.com. Follow him on Twitter @Timberry.