We play tricks on ourselves, Woody Zuill says. We think that we estimate because it gives us control. In reality, we estimate because we fear losing control. The irony, of course, is that we aren't in control: estimates are inaccurate, decisions are still based on them, commitments are also based on them, projects overrun, commitments are broken, costs spiral, ...
Spending more time estimating typically doesn't make us better at estimating but it does take time away from doing.
Zuill's experience is that it's possible to build software without any estimates by taking an important piece of functionality, building only the absolutely critical pieces of it, and then putting it in front of someone. The doing, and the review of what's been done, will help to determine what should be done next.
Sounds simple? Yes, but it's not easy. It's crucial to find allies and customers who are ready to accept it.
Here's my tidied-up sketchnotes from Woody's Beyond Estimates talk last night at Cambridge Agile Exchange.