Unpredictable. Unfocused. Just like life.

Pragmatic Marketing comments on this question:

Can anyone identify great software that was developed with a formal requirements process?

Railing against requirements is often another way of railing against poor product management. Too often, product managers are trying to document their opinions of a successful product. Students of Pragmatic Marketing have learned that product managers are messengers for the market. They know that "your opinion, although interesting, is irrelevant." Product managers should bring market facts to the planning session instead of their opinions. And most of all, they should put those facts into context with problems, use scenarios, and personas.

That may be the case for successive iterations of a product. However, truly great software, and truly great products in general solve a problem that customers didn't know they had. Or make our lives easier in ways that we could not have foreseen. Understanding the market for something that doesn't exist yet is a fool's game. What would a customer have said 10 years ago about giving their sales information to someone else. Yet today many companies use Salesforce.com.

Of course there does exist some basic requirements or a back of the napkin sort, but the formal requirements process doesn't usually pop up until a little later. In most startups, one person might wear that hats of engineer, product manager, and salesperson.