The partners spent one year preparing their business plan, which defined just what type of products they were looking for. Then they spent 18 months talking to consumers to determine what benefits they wanted. They were only ready to start spending the money to introduce their product once they knew they were giving consumers exactly what they wanted.
In the 20-plus years I've been working with inventors, by far the biggest mistake I see is people spending their money first and then finding out, after trying to sell their product, that they still need to make a few changes to meet the needs of their consumers. Often these inventors don't have enough money left to make the necessary changes.
Proper planning is a lesson every inventor should learn. Research all the details of your invention before you start spending your money, and you're more likely to get your product successfully launched.