I'm assuming this is for building a product, in which case the "why" is specced by market demand, and the "what" is little more than a goal of the product/featu

I'm assuming this is for building a product, in which case the "why" is specced by market demand, and the "what" is little more than a goal of the product/feature - such as "product to allow consumers to record their taxes". The "how" is obviously more involved and includes things such as technology choices and specs on what the customer will interact with and how data will be stored. The "what" would also often include essential features, such as "visual graphs or charts over time". These features would grow (or shrink) over time based on market feedback and testing. You rarely want your programmers/designers/QA defining the "why" behind your product. If it's a startup, you're generally creating your business because of the "why" - you don't start a company and then use the company to find a "why". If it's an established company creating a new product, you'd have had market research and similar groups set up before the product even started to identify the "why".