They spend too much on sales and marketing before they’re ready. Many venture companies move to a high burn rate too quickly and it’s hard to go back. Sometimes even a frugal entrepreneur winds up spending too much either because he doesn’t manage the money or is tempted by having money in the bank. This often happens when a startup raises too much money too early.

Other times, this occurs with entrepreneurs who are accustomed to having lots of resources. They ramp up sales before the product is ready. Of course, there’s a lot of work required to get sales early on. But a product with a truly great value proposition that delivers in a measurable way will practically sell itself. Companies that ramp sales and marketing too soon waste a lot of money.

Sometimes even when the product is great, the sales process itself isn’t understood to a point where it can be scaled: who are you selling to, how much will they really spend, and what profile of sales person does the company need to hire who will succeed at selling that particular product. All of this has to be understood before sales can efficiently scale.

Spending on the sales and marketing operations means there is no return if customers don’t bite. When you spend money on the product that work can be leveraged in future versions. (In fact, the key to effective product delivery is to try a lot of things and see what sticks.) For every venture dollar invested, I estimate that more than two-thirds go into sales costs and only a third into product development. Once you up the burn rate, there’s no easy way back.