If you’re starting a business, you need a business plan. That doesn’t mean you should hide away in a library for months writing 40+ pages of text. A plan should take you three weeks or less, and you should use a presentation format for speed, flexibility and impact. But you need a plan, and here’s why:

1) To prevent unpleasant surprises. When you start a company, you put your time, money and reputation on the line, doing something intrinsically tough to predict. The last thing you want to do is wake up a year or two down the road and realize you were doomed to fail from the start, because you didn’t ask yourself a few basic questions.

2) To counterbalance your emotions. At times during your startup experience, you’ll be manic – so passionate about your ideas you lose sight of reality. At other times, you’ll be overwhelmed by doubt, fear, or exhaustion. When your emotions get the best of you, having a business plan lets you step back, and take an objective look at what you are doing and why, what you know for a fact and what you are trying to figure out.

3) To make sure everyone’s on the same page. Chances are, you are not building a company by yourself. Ideally, you’ll have partners, so you can launch faster, smarter, and with less need to pay employees or suppliers. Even if you don’t have partners, you’ll have family, friends, and advisors involved. A business plan gets you and your team aligned, so they can provide help and support.

4) To raise capital. If you raise or borrow money – even from friends and family – you’ll need to communicate your vision in a clear, compelling way. A good business plan will help you do just that. A study by Babson College found that startups with a business plan raised twice as much capital as those without a business plan within their first 12 months.

Agree? Disagree? Got more reasons to create a plan? Please share.