(Editor’s note: Serial entrepreneur Steve Blank is the author of Four Steps to the Epiphany. This story originally appeared on his blog.)

Entrepreneurs hear that VC pitches ought to be short, 10-20 slides.  What most don’t know is that there is no way they can deliver a presentation that short by just “writing” the slide deck.

An entrepreneur I’ve known for a long time came by my ranch over Thanksgiving break to show me the first pass of his new startup slide deck.

My eyes were glazed by slide 9.

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It was over 35 slides long, with each slide feeling like it had 12 lines of 10-point type. It had a problem statement going back to the invention of the telephone, an opportunity claiming to exceed the Gross National Product and it had every possible product feature with enough left over for three other startups products.

My first reaction was, “you got to be kidding.” Yet I was hearing the pitch from an experienced entrepreneur with multiple wins under his belt. He had raised money from name-brand VC’s in past startups and knew what a fundable VC slide deck looked like.  What was going on?

Then I remembered, every slide deck I ever wrote started out just like this.

Most startups ideas are not built in an afternoon, typically they are the sum of seemingly disparate and discrete pieces of information, and a pattern recognition algorithm continuously running in a founder’s head. What I was seeing was an entrepreneur using a slide deck as a way to collect his thoughts.  The slides were his brainstorming tool.  He was using them to think through the impact of the idea he had, and was trying on for size the potential opportunity and trying to use the slides to spec his features.

The difference between this entrepreneur and a novice was that he knew his presentation wasn’t ready to show to a VC; he was using it to share his thinking with me to get more feedback on his business model.

We talked about how much of his presentation were just hypotheses (most but not all,) what hypotheses he could quickly test outside the building (assumptions about minimum feature set, pricing and customer archetypes) and how to turn some of the hypotheses into facts.

I pointed him to my “Lessons Learned” slide decks that turn a standard VC pitch into something more informative.  He left with both of us knowing that he was months away (and lots of customer feedback) from being ready for a VC pitch.

Most of the advice founders get about Venture Capital slide decks comes from the recipients of the presentations – the VC’s – letting you know how they want to see the final deck. And most of their recommendations are essentially “show us your business plan in PowerPoint.” Few VC’s have experienced the process a founder uses to get their idea into 10-slides. And none of them tell you how.

If you find yourself trying to shoehorn your 35-slide presentation into a “VC-ready” format, you don’t know enough yet. And you won’t know any more by sitting in your office surfing the web and writing more slides.

Get out of the building and talk to potential users and customers. The irony is the more you know, the easier it is to make your presentation short and concise.